200 Cincinnati Society of Natural History.

LOCOMOTOBY APPENDAGES OF TBILOBITES.

By JOHN MICKLEBOROUGH, Ph. D.

Principal, Cincinnati Normal School.

The discoveries and investigations of paleontologists touching thequestion of ambulatory and branchigerous appendages of the Trilo-bites, have been entirely ignored by many of the ablest workers in thescience. The important evidence which Mr. Billiugs produced wasunsatisfacto^ to both Dana and Verrill. In 1881, after many yearsof untiring labor, Mr. C. D. Walcott (in the " Bulletin of the Museumof Comparative Zoology at Cambridge College") furnished most con-clusive proof of the existence of appendages to the cephalic, thoracic,and abdominal divisions of Calymene, Cecaurus, and Acidaspis. Hesays: "the discoveries have been received in about the same manner"as those of Billings and others—with incredulity, and as " having littlevalue."

To confirm the conclusions of these naturalists, who have affirmedthe existence of Trilobite legs, and possibly shed some light on thecharacter of the ventral surface of these crustaceans, and thereby aidin the determination of ichnological specimens, is the object of thewriter. The conclusions here reached are based upon the work ofpredecessors, and the specimens of Asaphus megistos (Figs. 1 and 3),which were found by Mr. James Pugh (they now belong to Mr. DavidMcCord), two miles north of Oxford, Ohio, in the upper portion of theHudson River Group.

Although Ch. Mortimer, as early as 1750, and Linnseus, in 1753, haddetermined the crustacean character of the Trilobites, at least, inzoological affinities, they were placed with Limulus, yet more than acentury elapsed before any discovery of feet or antennae was made.In 1864, Mr. Billings discovered the presence of legs in a specimen ofAsaphus platycephalus, from the Trenton limestones of Canada.

To show the distrust in the minds of naturalists, we quote from thepamphlet of Mr. C. D. Walcott, page 196: "The instances of the dis-covery of the animal other than the dorsal shell and hypostoma arerare. M. Barrande, in reviewing the reported discoveries made of theappendages of the Trilobites to the date of the publication of hisVolume I., 1852, says: ' Unhappily, all the researches have resulted innothing more than the discovery of the pieces of the mouth namedHypostoma and Epistoma,and the intestinal canal.' Again, in hissupplement to Volume I., 1872, he says: 'The few scattered observa-

Locomotory Appendages of Trilobites. 201

tions of parts found which might belong to the Trilobites have littlevalue, and were accepted as such by naturalists.'"

In 1872, Dr. A. S. Packard, in his work on the Development ofLimulus polyphemus, page 185, says: "Though disposed to regardthe processes figured by Mr. Billings as feet, still the proof is unsatis-factory. The Trilobites probably had habits similar to those ofLimulus, and consequently they must have had ambulatory feet,rather than phyllopodal feet, attached to the middle segments of thebody. In view of the conflict of opinions as to the nature of thelimbs of the Trilobites, it is to be hoped that the matter will not besuffered to rest here by paleontologists, even if the most unique andvaluable specimens have to be sacrificed in making the requisite ob-servations."

In 1874, Mr. S. A. Miller figured and described, in the QuarterlyJournal of Science, an ichnolite which he regarded as the track ofAsaphus. In 1880, he reviewed the work of 1874, and figured and de-scribed another slab, the markings of which he regarded as made byan animal generically related to the former.

In 1875, Prof. Dana, in his Manual of Geology, page 123, says: "Noremains of legs are found with anj Trilobites."

In 1876, Dr. Nicholson, in his Manual of Zoology, page 219, says:" No traces of ambulatory or natatory limbs, of branchiae or of an-tennae, have ever been discovered. On the under surface of the bodynothing has hitherto been discovered except the hypostoma or labrum.It has generally been supposed that the axial lobes protected a seriesof delicate respiratory feet; but this view is doubted by manyauthorities, and the question is one which we have at present no meansof deciding."

In 1878, Prof. Huxley, in his Anatomy of Invertebrate Animals,page 220 (Am. Ed.), says: "Limbs or appendages capable of effectinglocomotion are always attached either to the head or to the thorax—-the extinct Trilobites possibly form an exception to this rule." Again,page 224: " Now, among the water-breathing Arthropoda no trace oflimbs has yet been certainly discovered among the Trilobites."

In the Encyclopedia Britannica, ninth edition {vide Crustacea), Mr.Henry "Woodward, F.R.S., says: "At present more evidence is neededas to the nature of the locomoLory appendages of this extinct group—Trilobita."

In a letter from Mr. C. D. Walcott, dated June, 1883, he states thatall his recent sections "simply corroborate the views given in hispamphlet of 1881."

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These numerous references and quotations are given to show thedistrust and uncertainty in the minds of prominent naturalists as tothe limbs of the Trilobites.

In the autumn of 18S2 the Trilobite, Asaphus megistos (Fig. 1),was sent me for examination. In the delay of correspondence withpaleontologists, fortunately, no report was made, for in the spring of1883, twelve months after finding the first specimen, the same partyfound the second, which proved to be the matrix of the ventral sur-face of the first specimen. It was found about one hundred metersfrom the point where the first was obtained.

About two thirds of the cephalic shield is broken off. That part ofthe head anterior to a line drawn obliquely through the left eye to themiddle of the pleura of the second thoracic somite on the right is en-tirely wanting. With the head restored, the specimen would be about18.5 centimeters (7f inches) long; in width, 11.5 centimeters (about4£ inches). On the ventral surface (Fig. 1) a broad median grooveextends along the concavity of the thorax and abdomen. It beginsat a point beneath the articulation of the head with the thorax, or inthe posterior part of the area between the lobes of the hypostoma.Its length is 10.5 centimeters (4-| inches)—6.5 centimeters being thelength of the thoracic, and four centimeters that of the abdominalportion of the groove. This specimen clearly demonstrates the con-cavity of the three principal divisions of Asaphus, a fact which Mr.Billings pointed out in 1864. The vertical distance from the dorsalsurface of the head to a line in the plane of the external margins ofthe pleurae is 2.5 centimeters (about one inch).

Directly beneath the eight somites of the thorax, ten pairs of jointedlimbs are distinctly seen; the two anterior pairs of appendages aresituated directly under the first two thoracic segments; but from thecharacter of these appendages, as well as the relation ot parts, these,while having the general appearance of organs of locomotion, yetwere, no doubt, maxillipedes with the basal joints articulated to thebody of the animal, near the point where the oral aperture certainlyexisted, and presumably they were differentiated to perform the func-tion of mouth organs, and consequently should be considered asbelonging to the cephalic division. The remaining eight pairs of legsare then directly referable to the eight thoracic somites. The numberof joints in a limb can not be definitely given from a study ot* thesespecimens; the basal joints are not preserved at the median groove.

Following the terminology of Milne-Edwards for the several partsof the limb of a crustacean, the prominently-marked portion of theseambulatory limbs is undoubtedly the meropodite, which was in some

Locomotory Appendages of Trilobites. 203

cases two centimeters in length and quite large, with the mero-carpopo-dite articulation well pronounced, so as to leave a distinct, pit-likedepression in the matrix. The several joints externally to that whichis considered the meropodite can be distinguished by careful study ofthe several legs and the grooves and fovese of the matrix. The car-popodite was about the length of the meropodite, but decidedly slenderas compared with the latter. If there was any positive evidence toshow that these were broad, lamellar appendages, adapted to swim-ming, then the slender joints external to the meropodite might beaccounted for by supposing the edges were the portions visible. Thepropodite was about two thirds the length of the carpopodite, andalso appears to have been slender and slightly curved backward; thedactylopodites are not well preserved, yet sufficiently so to permit theconclusion that they were not chelate. The posterior pair of thesethoracic appendages is directly beneath the posterior somite of thethorax. The meropodites of the two anterior pairs of appendages, asshown in fig. 3, resemble the same joints in the thoracic limbs.

In examining the matrix, fig. 3, d!, where the left limb of the anteriorpair is well preserved, it is seen to curve around the outer margin of theleft lobe of the hypostoma, and from the evidence which the surface pre-sented when first examined, I am of the opinion that this limb waschelate. In removing the limestone so as to expose the left lobe of thehypostoma, and also establish the articulation of the claws, an acci-dental stroke destroyed the evidence of this direct connection, yet atthe fracture the ends of two broken claws can yet be seen. At first Iwas disinclined to regard the distal extremity of this pair as chelate.Before attempting to remove the limestone, the surface clearly showeda conjunction of these parts. This condition could have been ac-counted for by supposing one limb to have been thrown over another.It was to clear up this point that the removal of the adhering materialwas made. If chelate, the claws were slender and of about equal sizeas in Limulus. As the hypostoma is frequently found in this limestoneformation, it is to be hoped that these limbs will also be found, so asto definitely settle this point. On fitting the two specimens togetherthe ends of these supposed claws are seen at the fracture directly be-neath the left eye. These specimens demonstrate that the thoracic ap-pendages were well developed, walking legs extending nearly to theouter margins of the carapace. The exoskeleton of the limbs seems tohave been somewhat different in character from the calcareous exoskele-ton of the dorsal surface of the animal. At least, it was of such acharacter as not to preserve well the integrity of the parts in the pro-cess of fossilization. They could not have been soft and }Tielding, judg-

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ing from the symmetry of the matrices of the Meropodites, as well asfrom the general cylindrical character of limbs themselves.

On the ventral surface of the p3'gidium there are at least twelve(pairs of) appendages; posteriorly, an exact enumeration is impossible.The term pairs is used on account of the median groove, showing inthe structures a bilobed character. This groove is continuous withthe thoracic groove, and is somewhat narrower and more shallow thanthe latter. From an examination of the two specimens, these twelveor more appendages appear to be leaf-like, or foliaceous, and on eachside of the median groove the direction was outward and somewhatforward. No doubt these appendages were branchial in function, andalso adapted to swimming.

These specimens will prove of interest to zoologists, especially froma taxonomic point of view. Spence Bate and Heniy Woodward, ofEngland, and Prof. Dana, of this country, regard the Trilobites asclosely related to Isopoda. Woodward homologizes thus:

TEILOBITA (fossil or extinct).1. Eyes sessile, compound.2. No ocelli visible.3. Appendages partly oral, partly am-

bulatory, arranged in pairs.4. Thoracic segments variable in num-

ber, from six to twenty-four, free, mov-able ; animal sometimes rolling in a ball.

5. Abdominal somites coalesced, form-ing a broad caudal shield, bearing thebranchise beneath?

6. Lip-plate well developed.

ISOPODA (fossil and living).1. Eyes sessile, compound.2. No ocelli visible.3. Appendages partly oral, partly am-

bulatory, arranged in pairs.4. Thoracic segments variable in num-

ber, from six to twenty-four, free, mov-able ; animal sometimes rolling in a ball.

5. Abdominal somites coalesced, form-ing a broad caudal shield, bearing thebranchiae beneath.

6. Lip-plate small.

If the conclusions herein expressed in the interpretation of theabdominal appendages of Asaphus megistos are correct, then the markof doubt in No. 5 of Woodward's homological table may be removed.

Prof. E. Van Beneden, of Belgium, believes the Limuli are not crus-taceans, and, from a study of their embryology, concludes that theycan not be separated from scorpions and other arachnida. This view,in which he is.not alone, if correct, would carry the Trilobites out ofthe class Crustacea.

Dr. Packard, in his excellent work on the " Development of Limuluspolyphemus," places the Xiphosura and Eurypterida as suborders underthe order Merostromata, which is followed by Trilobita as a separateorder. This view is accepted by Dr. Lockwood and Mr. C. D. Walcott.It remains for zoologists to place whatever value may attach to thefact of the appendages of Trilobites subserving the purposes of bran-chial organ, of manducation, and of locomotion, either ambulatory ornatatory.

Fig. 2,FIG. 1.—Natural size, a a, meropodites of anterior pair of appendages,— maxillipedes;

b b, eighth pair of (thoracic) legs ; c, articulation between carpopodite and propodite ;d, articulation between propodite and dactylopodite ; e, branchigerous organs beneathpygidium.

Fig. 2.—The specimens 1 and 3 fitted together, and reduced to nearly one third nat. size.

FIG. 3.—a a, matrices of meropodites of anterior pair of appendages ; b b, matrices ofeighth pair of legs ; c, branchigerous appendages ; d, left maxillipede, probably chelate ;e, left lobe of hypostoma.