80 The Ottawa Naturalist. [Oct. 



projecting inwardly from the last preserved marginals do not 

 extend through to the aboral surfaces of the plates, but thev 

 served for attachment of the epineurals. We may still see that 

 the 3rd and 4th marginals on the left each possessed two of these 

 bosses though the corner ones have been nearly lost by weather- 

 ing. 



IX. Where adambulacra possess long vertical axes these 

 are usually somewhat imbricated, the oral ends being tipped 

 toward the mouth, never away from it. The broken ends of 

 rays II to V all show this inclination. See stereogram in [C] 

 ray V and our plate IX, figures 1 and 2. The angle of inclination 

 is about 2 5. The slight imbrication is an adaptation to secure 

 greater flexibility in the arms and to help in thrusting the food 

 content of the furrow toward the mouth. Such evidence cannot 

 be lightly set aside. 



Epineurals. 



Although asserting that the "covering pieces" had their 

 origins in the pits of the oppositely placed adambulacra, Dr. Ray- 

 mond calls them "alternating plates" (p. 105, line 6). A study 

 of their distal ends is of interest. The younger pieces, plate VIII, 

 fig. 2, meet, though very irregularly, by their end faces. The 

 furrow here is in a contracted condition, and this should have 

 opened the end faces, were these ambulacra, and displayed the 

 muscle fields of the transverse dorsal ambulacral muscles. Not 

 the least trace of such muscles is anvwhere to be seen. 



The older epineurals, following the law of biogenesis, are 

 less like primitive covering pieces and meet only by their inner 

 edges, plate VIII, fig. 1. The fallen 8th, the covered" 5th and the 

 two shifted 3rds in this figure indicate that the meeting ends 

 were free. 



The varied imbrication of the sides of these pieces and the 

 absence of traces of longitudinal muscles is also evidence against 

 their being ambulacra. 



The epineurals marked as first could by no possible means 

 have had their distal ends bound to their opposite neighbors. 

 To conceive these first members of a series as ambulacra is 

 therefore wholly out of the question. 



The evidence of plate IX, fig. 2, is that the epineurals were 

 borne by the marginals. The latter plates have lost much of 

 their original surface, but there is here and there a suggestion 

 that they also bore large spines outside of the epineurals. For 

 one instance note the structure of the raised central portion of 

 the more perfectly preserved fifth marginal in plate IX, fig. 2. 

 The only spine fragment preserved in the matrix, however, is in 



