ZOOLOGICAL (II LB LCTERS. 



127 



Phasnoschisma. The hydrospire-clefl Is rather less constricted in 0. pentangularis 

 (compare figs. 4 & 10 on PI. XV.), and from the latter type it is an easj transition 

 to 0. Puzos and 0. Orbignyanus (PI. XIV. tigs. 14-18). But for the relatively large 



size of the deltoids and their appearance externally above the truncated radial limbs 



there is really nothing to separate these two species from I'htt nuschisma P. Arckiaci, 

 perhaps, being the type which approaches them most closely (PI. XII. fig. 10). 

 Codaster only differs from Phcenoschisma in the absence of hydrospires in the poste- 

 rior interradius (IT. XII. tigs. 1, 4 ; PL XIII. rigs. 1, 4) ; while Phcenoschisma caryo- 

 phyllatum would be a Oryptoschisma if it had a broader summit and its ambulacra 

 were a little wider so as to completely conceal the hydrospire-slits (PI. V. tigs, 2.'!, 

 24; PI. XIII. tig. 20; PL XIV. figs. 1-4). Put there is no sort of resemblance 

 between Oryptoschisma and Phasnoschisma while (PL XI. figs. 1-4), with which 

 P. caryophyllatum is linked by several intermediate forms. 



The principal resemblances and differences between the various genera of the 

 Pentremitida', Troostoblastidtt, Nucleoblastidae, and Orqphocrintis are conveniently 

 shown in the following Table. 



Closely related, however, as are most of the regular Blastoids to one another, our 

 morphological inquiries have led us to believe that they represent more generic types 

 than have hitherto been recognized. On the other hand, we have come to the con- 

 clusion that the variations of individual specific forms are unusually extensive, and 



