128 



PANAMIC DEEP SEA ECHINI. 



There are great differences in the number of plates of the odd an- 

 terior ambulacrum : in P. Jefreysi we find thirteen to fifteen pairs, Fig. 

 178 ; in P. Tanneri twelve, Fig. 179 ; in other genera of Pourtalesiae, as in 



4 I 1 



48 mm. 



Fio. 177 *. Spatagocystis Challengeri. 



IV" a 



Fig. 178. Poi rtalesia Jeffretsi. 



Aftbb Lot£m. 



Echinocrepis, there are twenty-one to twenty-two, Fig. 180; and in Spatago- 

 cystis, sixteen pairs. Fig. 181. The number of the plates is due mainly to 

 tlie length of the actinal pouch in those genera. These differences are 

 well shown on comparing the profiles of the actinal pouches of P. Jeffreysi,^ 

 of P. carimfa,'' Fig. 182, of P. Tannen (PI. 57, fig. ^), of P. hisjnda,^ of 



i(j lum. 



Fig. 179. P. Taxxehi 



92 mm. 



Fig. 180. Echinocbkpis setiorra. 



Fig. 181. Spatagocystis Challengeri 



P. cera/opy(/a* of Echinocrcpis sefigera (PI. 60, fig. •), and Spataffoet/stis 

 Challengeri (PI. 71, fig- -)• These profiles differ greatly in outline, especially 

 in the angle formed by the groove with the actinal system, as well as 



1 Lovcn, Tourtalesia, PI. Ill, fig. 12. 



2 Lovoii. PI. VI, fig. 4."); "Cliallengor" Echinoidea, PI. XXVIIIV fig. 11. 

 •* "Challenger" Echinoidea. PI. XXII, fig. 8. 



* "Challenger" Echinoidea, Pi. XXVIII, fig. 5. 



