THE APPENDAGES., ANATOMY, AND RELATIONS OF TRILOBITES. 



1918, pi. 26, figs. 8, 14, 15; pi. 27, figs. 1-3, sa, 6-9, 12 (not Calymene), (not 15, Calyinene) ; pi. 28, figs. 1-5; 

 pi. 34, fig. i; pi. 35, fig. 7. Milne-Edwards, Ann. Sci. Nat., Zoologie, ser. 6, vol. 12, 1881, pi. 10, figs. 1-18. 

 Bernard, The Apodidae, 1892, text figs. 46, 51. 



Cephalic Appendages. 



No trace of antennules has yet been found. 



I. find only three sections cut through the plane of the hypostoma of Ceraurus which 

 show anything of the cephalic appendages, and no one of them is very satisfactory. The 

 best is No. 22, the one figured by Walcott (pi. 3, fig. 2, 1881 ; pi. 27, fig. 12, 1918), but 

 one should remember that this section is not actually cut in the plane of the hypostoma but 

 is a slice diagonally through the head, cutting through one eye and the posterior end of 

 the hypostoma. It shows what seem to be the coxopodites of the second, third, and fourth 

 pairs of cephalic appendages, the exopodites of the third and fourth pairs, and the metas- 

 toma. If this interpretation is correct, the first pair of gnathites lay alongside the hypos- 



Fig. 17. Transverse section of Ceraurus 

 pleurexanthemus, showing the relation of 

 the coxopodite to the appendifer. Traced 

 from a photographic enlargement of the 

 slice. Specimen 128. X 4-5- 



Fig. 18. Slice of Ceraurus pleurex- 

 anthemus, showing a nearly continu- 

 ous section of an endopodite and an 

 exopodite above it. The latter is so 

 cut as to show only the edge of the 

 shaft and the bases of a few seta:. 

 Traced from a photographic enlarge- 

 ment. Specimen in. X 4- 



toma or under its edge, and were feebly developed, the second pair were attached in front 

 of the tip of the hypostoma, curved back close to it, and their inner ends reached the sides 

 of the metastoma. The third and fourth pairs were back of the metastoma, the third 

 pair was stronger than the second, and the fourth probably like the third. 



Specimen 92 shows traces of the slender endopodites belonging to the cephalon, but no 

 details. Specimen 22 shows on one side exopodites (epipodites of Walcott) belonging to 

 the third and fourth cephalic appendages. That belonging to the third shows some long 

 sete and a trace of the shaft, while the one on the fourth appendage (third coxopodite) has 

 a portion of a broad shaft and a number of long setse. It should again be remembered 

 that the slice does not cut through the plane of the exopodite, but across it at a low angle, 

 so that a part but not all of the shaft is shown. On the other side of this slice there is a 

 fairly good section of one of the thoracic exopodites. It is, however, turned around in 

 the opposite direction from the others, as would be expected in an enrolled specimen. 



Specimens 4 and 5 (pi. i, figs. 4, 5, 1881) are slices cut diagonally through the head 

 of Ceraurus, in front of the posterior tip of the hypostoma. They show fragments of 

 endopodites and exopodites which may be interpreted as practically identical in form with 

 those of the thorax. Due to the diagonal plane in which the section is cut, slice 5 shows 



