52 THE APPENDAGES, AN ATOM Y^ AND RELATIONS OF TRILOBITES. 



i, possesses slender appendifers. Two other specimens (Nos. 237 and 242) show them 

 quite well. They were probably present in all trilobites, but seldom preserved. The appen- 

 difers have the same origin as the entopophyses of Limulus, and like them, may have rela- 

 tively little effect on the dorsal surface. 



Calymene senaria Conrad. 

 (Text figs. 13-16, 23.) 



Illustrated: Walcott, Bull. Mus. Comp. Zool., .Harvard Coll., vol. 8, 1881, pi. I, figs. 6-10; pi. 2, figs. 5-7, 

 10; pi. 3, figs, i, 3, 8-10; pi. 4, figs, 3, 7; pi. 5, figs. 1-6; pi. 6, figs. I (restoration), 2; Proc. Biol. Soc. 

 Washington, vol. 9, 1894, pi. i, fig. 7 (restoration); Geol. Mag., dec. 4, vol. i, 1894, pi. 8, figs. 7, 8; 

 Smithson. Misc. Coll., vol. 67, 1918, pi. 26, figs. 1-7, 9-13; pi. 27, figs. 4, 5 (not sa), 11 (not 12, Ceraurus), 

 13, 14, 15 (not Ceraurus") ; pi. 28, figs. 7, 8; pi. 33, fig. i (restoration); pi. 34, fig. 2; pi. 35, fig. 6. Dames, 

 N. Jahrb. f. Min., etc., vol. i, 1880, pi. 8, figs. 1-5. Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 

 1881, pi. n, figs. 19-32; pi. 12, figs. 33-41. Packard, Amer. Nat., vol. 16, 1882, p. 796, fig. 12. Bernard, The 

 Apodidse, 1892, text figs. 50, 52, 54; Quart. Jour. Geol. Soc., London, vol. 50, 1894, text figs. 13, 15, 17. 

 CEhlert, Bull. Soc. Geol. France, ser. 3, vol. 24, 1896, fig. 12. Beecher, Amer. Jour. Sci., vol. 13, 1902, pi. 

 5, fig- 7. 



In both of Walcott's accounts (1881, 1918) of the appendages of Calymene and 

 Ceraurus, he has described them together, so that those who have not taken time to study 

 the illustrations and disentangle the descriptions are very apt to have a confused notion 

 in regard to them. I have therefore selected from the original specimens those slices of 

 Calymene which are most instructive, and bearing in mind the probable appearance of the 

 appendages of an enrolled Triarthrus, have tried to interpret them. In such a method of 

 study, I have of course started with a pre-formed theory of what to expect, but have 

 tried to look for differences as well as likenesses. 



Cephalic Appendages. 



Antcnnules. The evidence of antennules rests on a single slice (No. 78). The appen- 

 dage in question is exceedingly slender and arises at the side of the hypostoma near its 

 posterior end. It shows fine, slender segments, and curves first outward and then forward. 

 If it is in its natural position, it is not an antennule, but the endopodite of the second or 

 third pair of cephalic appendages. It is short, only about one-third the length of the hy- 

 postoma, but is doubtless incomplete. The two distal segments show a darker filling, indi- 

 cating that they were hollow. Judging from analogy with other trilobites, the appendage 

 is probably an endopodite and not an antennule. There can be no reasonable doubt, how- 

 ever, that Calymene possessed antennules. 



Some idea of the form of the coxopodites of the cephalic appendages may be obtained 

 from sections which cut in approximately the plane of the hypostoma. Such sections are 

 shown in Walcott's photographs (pi. 26, figs. 4, 6, n, 1918). Specimens 50 (fig. 4, our 

 fig- : 3)> 5 1 (fig- 6), 6 (fig. n), and 40 (our fig. 14) agree in showing two pairs of slender 

 coxopodites which are attached at the sides of the hypostoma and run backward parallel and 

 close to it, and two pairs of larger coxopodites which are behind the hypostoma, although the 

 point of attachment of the third pair is in front of its tip. The anterior pair are appar- 

 ently under-developed and no longer function as mouth parts, while the posterior two pairs 

 are large and armed on their inner ends with spines. Specimen 78, which has already been 

 mentioned in connection with the antennules, shows a second very slender appendage back 

 of the so called antennule, which is equally slender, but is directed outward instead of for- 



