124 



PANAMIG DEEP SEA ECHINI. 



In Pilematechinus R'athbuni (PI. 85, figs. /, ..'), Fig. 1G4, the labium is 

 followed as in the younger C. Wi/viUii by two plates and the sternum is 



absent. This anomalous con- 

 dition is readily explained by 

 comparing the lain um and the 

 two plates with the primordial 

 plate and the [dates succeeding 

 it in the other interambulacra. 

 In Echinocrepis, Fig. 165, 

 the anterior interambulacral 

 primordials alone reach the 

 actinal system ; there is no 

 labium. 1 The sternum con- 

 sists of one plate followed by 

 two episternal plates, Fig. 167, 

 and further separated from the 

 anal system by three pairs of 

 small plates (PI. 68, fig. /). The sternum is separated from the actinal 



system by both rows of the posterior 

 lateral ambulacra, Fig. 108, and the 

 anterior zone of the lateral posterior 

 interambulacra, which extend beyond 

 the sternum, the first plates of which 

 are in contact with the actinostome as 

 well as the anterior lateral interambu- 

 lacra (PI. (38, fig. /). 



85 mm. 



Fig. 164. Pilematechinus Rathbuni. 



6 

 4 1 



92 mm. 



Fin. 165. Echinocrepis setigeba. 



Fig. 160. E. cuneata, 



After Lov£n. 



In the Pourtalesise there is not only an unexampled extension of the 

 posterior extremity, in which a prominent anal snout is formed, but also 



1 Though Loven, Pourtalesia, PI. VIT, figures one in P. cuneata, Fig. 166, its absence in E. setigera 

 is not remarkable, as iu P. Tanneri we find the same discrepancies. 



