180 



PANAMIC DEEP SEA ECHINI. 



Paleopneustes spectahilis de Meij. has, like the West Indian species P. c/is- 

 tatus, a very prominent marginal fascicle.^ These reciprocal relations extend 

 to the character of the tuberculation and of the spines. The coarse tuber- 

 culation of Paleopneustes, its extension over the actinal surface, both in the 

 ambulacral and interambulacral areas (Pis. 95 ; 97), are features character- 

 istic of embryonic stages already partly lost in Linopneustes, the actinal sur- 

 face of which is eminently Spatangoid, Fig. 294 (PI. 92), while the abactinal 

 surface (PI. 93) has the coarse tuberculation of Paleopneustes, with a subanal 

 plastron into which the posterior lateral ambulacral plates have extended, 

 restricting the odd interambulacral plates to a narrow zone in front of the 



140 mm. 



Fig. 265. 1 Paleopneustes cristatus. 



no mm. 

 2 LiXOPNErSTES LOXGISPINTS. 



anal system (PI. 92, fig. 2) ; in Paleopneustes the plates of the odd inter- 

 ambulacral zone extend of uniform width past the anal system (Pis. 95; 97). 

 Linopneustes (Pis. 92, fig. 1 ; 93) also has a slightly re-entering odd ambu- 

 lacral area extending from the apical system to the ambitus, where it becomes 

 more re-entering with increasing size (PI. 92), and extends to the actino- 

 stome. This gives to Linopneustes a more angular outline than to Paleop- 

 neustes, Fig. 265, the latter is more ovoid (PI. 97) and has no sunken 

 anterior ambulacral groove either on the actinal or the abactinal side. 



It is true that the outline of Pakojmeustes cristatus is more rectangular 

 and angular (PI. 95) than that of P. ht/strix (PI. 97), but in both there is no 



» •' Siboga" Echiiioidea, PI. VIII, fig. 87. 



