POURTALESLE. 



127 



4 la iV a 



which is narrow, small, elongate (Pis. 70, fig. 4; 71, fig. 6), by large com- 

 posite double plates of the lateral anterior interambulacra and by the 

 second rows of plates of the lateral poste- 

 rior ambulacra extending along the ster- 

 num, which also separate the actinal plates 

 of the lateral posterior ambulacra from the 

 actinal plates. 



The position of the anal system on the 

 actinal side in Echinocrepis and Spatago- 

 cystis materially alters the proportion of 

 the actinal plates of the odd interambu- 

 lacrum from those of Pourtalesia proper 

 and Plexechinus, in which the anus is in 

 a sunken groove at the base of a well 

 developed anal snout, round which a fas- 

 ciole is developed. Compare Figs. 107, 

 175 to Figs. 171, 174. 



The shape of the actinal system of 

 Pourtalesia Tanneri, Fig. 170, differs con- Fig- 175. Spatagocystis Challengebi. 

 siderably from that of P. Jeffreysi? and of 

 P. earina/a.- It is round in the former 

 (PL 57, fig. ■>), somewhat rectangular in 



m 



1G nini. 



Fig. 176. Pourtalesia Tanneri. 



4 a \ 1 I 1 6 

 92 mm. 



Fig. 177. Echinocrepis setigeba. 



the second, and oval in the third. In E. setigera the actinal system is pear- 

 shaped, Fig. 177, and pointed abactinally in Sj). Challengeri, Fig. 177 a . 



1 Loven, Pourtalesia, PI. IV, fig. 18. - " Challenger " Echinoidea, PI. XXVIII a , fig. 9. 



