280 CATALOGUE OF THE BLASTOIDEA. 



(PI. V. figs. 25, 26 ; PL XIV. fig. 10). In each alike, however, the hydrospire-slits 

 extend far up on the sloping sides of the radial sinus and are crossed by the radio- 

 deltoid sutures, the deltoid plates not appearing externally except in abnormal 

 individuals (PI. V. fig. 24). 



In Orophocrinus, on the other hand, the deltoids appear on the exterior of the 

 calyx above the truncated ends of the radial limbs (PI. XL fig. 9 ; PL XIV. figs. 14- 

 18; PI. XV. figs. 1, 3, 6), and the width of the radial sinus is so much reduced 

 that the hydrospire-slits come to be concentrated at its deepest part and are not 

 visible unless the lancet-plates are removed, and not always then (PI. XL fig. 9 ; 

 PI. XV. figs. 4, 8, 10, 13). In the two Belgian species, however, the radial sinuses 

 are relatively wider, and parts of the hydrospire-slits are visible on their sloping 

 sides, even when the ambulacra are preserved (PI. XIV. figs. 14-18). But there is 

 such a close relationship between them and the two other European species 

 (PI. XIV. figs. 4, 10) that it would be impossible to refer them to Plicenoschisma, 

 apart from the fact that they have deltoid plates appearing on the exterior of the 

 calyx, and the anus distinct from the posterior spiracles. 



The mutual relations of Cryptoschisma and Orophocrinus may be expressed as 

 follows : — 



Deltoids invisible externally. Spiracles small, the^ 

 posterior pair confluent with the anus. 



Hydrospire-slits on the sloping sides of the radial y Cryptoschisma, E. & C. 

 sinuses, but completely concealed by the wide 

 ambulacra. 



Deltoids visible externally. Spiracles (when present) ") 

 ten linear openings, the posterior pair separate 

 from the anus. >• Orophocrimts, von Seebach. 



Hydrospire-slits generally concealed and mostly con- 

 centrated at the bottom of the radial sinuses. 



Genus CRYPTOSCHISMA, gen. nov. 



Pentremitidea, d'Orb. (pars), Prod. Pal. Strat. 1849, torn. i. p. 102. 



1 >vntmnitid<ea, d'Orb. (pars), Cours element. Pal. et Geol. 1852, torn. ii. fasc. 1. p. 139, fig. 1. 



Pentatrematites Truncati, Roemer (pars), Archiv f. Naturgesch. 1851, Jahrg. xvii. Bd. i. 



p. 368. 

 Pentremitidea, E. and C. (pars), Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 220. 



Gen. Char. Calyx elongated, with a broad, flat, and truncated summit. Radial 

 6inuses wide and open, their sloping sides pierced by hydrospire-slits, which are 

 completely concealed by broad and petaloid ambulacra. Spiracles single or rarely 

 double, but in the latter case the posterior pair are confluent with the anus. 



