5 6 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



the length of the cephalon, and to a point a little behind the second glabellar furrow from 

 the back of the head. 



In Doctor Walcott's restoration of Calymene he has represented all four pairs of bira- 

 mous appendages as articulating back of the posterior end of the hypostoma. I think his 

 sections indicate that the gnathobases of two pairs of these appendages rested alongside or 

 beneath it, and in particular, the longitudinal sections (1881, pi. 5) would appear to show 

 that the mouth was some distance in advance of its posterior end. 



Restoration of Calymene. 

 (Text fig. 1 6.) 



From what has been said above, it is evident that for a restoration of the appendages 

 of Calymene considerable dependence must be placed upon analogy with other trilobites. 

 Nothing is positively known of the antennules, the exopodites of the cephalon, or any ap- 

 pendages, other than coxopodites, of the pygidium, but all were probably present. It is 

 inferred from the slices that the first two pairs of cephalic appendages were poorly devel- 

 oped, the endopodites short and very slender, the coxopodites lying parallel to the sides of 

 the hypostoma and nearly or quite functionless. The gnathites of the last two pairs of 

 cephalic appendages are large, closely approximated at their inner ends, and bear small 

 tooth-like spines. The endopodites are probably somewhat better developed than the an- 

 terior ones and more like those on the thorax. 



The coxopodites of the thorax appear to have had nearly cylindrical endobases which 

 tapered inward. The endopodites were slender, tapering gradually outward, and probably 

 did not extend beyond the dorsal test. Small spines were present on the distal end of 

 each segment. Each exopodite had a long, slender, unsegmented shaft, to which were at- 

 tached numerous long, overlapping, flattened setas. The shaft may have been angulated 

 near the proximal end, and may have been directed somewhat forward and outward as 

 in Neolenus, but the evidence on this point is unsatisfactory. The number of pairs of ap- 

 pendages is that determined by Walcott from longitudinal sections, namely, four pairs on 

 the cephalon beside the antennules, thirteen pairs in the thorax, and nine pairs on the 

 pygidium. 



Calymene sp. ind. 



(PI. 6, figs. 4, 5-) 



Illustrated: Walcott, Bull. Mus. Comp. Zool., Harvard Coll., vol. 8, 1881, pi. 6, figs, sa, b; Proc. Biol. 

 Soc. Washington, vol. 9, 1894, pi. I, fig. 10; Geol. Mag., dec. 4, vol. I, 1894, pi. 8, fig. 10; Smithson. Misc. 

 Coll., vol. 67, 1918, pi. 36, figs. I, 2, 2a-d. Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881; pi. 

 12, figs. 443, b. 



In the United States National Museum there is a thin piece of limestone, about 3 

 inches square, which has on its surface eight jointed objects that have been called legs of 

 trilobites. Two of these were figured by Walcott (1881, pi. 6, fig. 5). The slab contains 

 specimens of Dalmanella and Cryptolithus, in addition to the appendages of trilobites, and 

 is said by Doctor Ulrich to have come from the tipper part of the Point Pleasant formation 

 (Trenton) on the bank of the Ohio River below Covington, Kentucky. 



The specimens are all endopodites of long slender form, similar to those of Triarthrus, 

 but since that genus does not occur in the Point Pleasant, it is necessary to look upon some 

 other trilobite as the former possessor of these organs. Both Isotelus and Calymene occur 



