70 



THE CYSTIDEA 



plate on the left, that is, opposite the anus. There was a slender stem 

 of circular columnals. Lysocystis, S. A. Miller (1889, proposed for Echino- 

 cystis, Hall non Wyville Thomson; syn. Scolocystis, Gregory, 1897), 

 Silurian, N. America. Theca sub-pentagonal, composed of four circlets of 

 plates. Aboral circlet of four (f) small plates, followed by two circlets of 

 five plates each, regularly alternating, and an adoral circlet, number un- 

 known. Apparently three free brachioles, possibly becoming five by the 

 usual bifurcation. Anus at adjacent upper angles of two plates of third 

 circlet. In the only known species the plates of second and third circlets 

 were strongly nodose. Stem unknown. 



-Br' 



FIG. XXXVII. 



Cryptocrinus. 1, from oral surface ; 2, enlarged view of oral region, the tegminal plates 

 removed; 3, abpral view; 4, side view. (All diagrammatised from Jaekel.) As, anus; fir', 

 facets for brachioles ; M, hydropore ; p, another pore ; Stf , facet for stem. 



ORDER 4. Diploporita, Zittel (1879, emend.) 



Cystidea in which radial symmetry affects the food-grooves, 

 and by degrees the thecal plates connected therewith, but not the 

 interradial thecal plates ; probably also the nerves and ambulacral 

 vessels, but not the gonads. The food-grooves are epithecal, i.e. 

 are extended over the thecal plates themselves without intermedi- 

 ate flooring ; they are also prolonged on to exothecal brachioles, 

 which line the epithecal grooves. The stereom of the thecal plates 

 may be thrown into folds, but the mesostroma does not so much 

 tend to lie in strands traversing the sutures, nor are pectinirhombs 

 or " pore-rhombs " developed ; diplopores are always present in 

 the mesostereom, but often restricted to definite tracts or plates, 

 especially in higher forms. 



While some descendants of the Aristocystidae were seeking in 

 vain to perpetuate their race by assuming the flattened carapace 

 of Anomalocystidae, and while others, becoming more reconciled 

 to a sedentary life, were stretching out from their mouths longer 

 and longer arms into the food-bearing sea, raising themselves too 

 on loftier columns, there were yet others that hit upon another 

 way of meeting the needs of a fixed existence. The chief need 

 was to expose food-collecting surface in greater amount and over a 



