THE CYSTIDEA 



which now form the third circlet, viz. in order, 14, 15, 10, 16, 11, 17, 

 12, 18, 19. The superficial resemblance of Cystoblastus to certain 

 Blastoids has led most 



writers to imagine a true .Sv' /Q\ v) 



relationship. This involves 

 the entire disappearance 

 of plates 5-9 ; the homolo- 

 gising of the plates here 

 called 10, 11, 12, and 14, 

 as well as the absent 13, 

 with plates 20-24, and the 

 consequent disappearance 

 of plates 10-14 also ; the 

 violent supposition that 

 the horizontal transverse 

 or tangential folds of the 

 demi-rhombs in Cystoblastus 

 originated the radial or 

 vertical folds of the hydro- 

 spires in Cadaster; as well 

 as such minor points as 

 the shifting of both anus 

 and hydropore, and the 

 fusion of two pair of basals, 

 neither of them the same 

 pair as composes plate 3 of 

 Cystoblastus. 



The structures of the 

 subvective grooves in the 

 more highly specialised 

 genera of this family have 

 often been spoken of as 

 "recumbent arms." They 

 differ, however, from the 

 arms of Crinoidea in origin 

 as well as recumbency. From 

 the subvective structures of 

 Glyptosphaeridae and Pro- 

 toblastoidea, they differ 

 in that the brachioliferous 

 plates are not thecal plates 

 or even intercalated be- 

 tween such plates, but lie 

 outside them and often 

 transgress their sutures. 



FAMILY 7. CARYOCRIN- 2 



IDAE. Rhombifera in which 



the theca is composed primitively of four circlets of plates, comparable to 

 the infrabasal (IB), basal (B), radial (R), and deltoid (A) circlets of a crinoid 



FIG. XXXIV. 



Pleurocystis filitex- 

 tus. 1, analysis ; 2, 

 view from antanal 

 side, restored from 

 original observations ; 

 3, view from anal side, 

 after Jaekel. 



