186 



ECHINODERMATA PELMATOZOA 



SUB-KINGDOM III 



Trochocystites, Barr. Calyx strongly compressed. Plates of the right and 

 left sides large, those of both the anterior and posterior small, polygonal. 

 All plates perforate, but without pore-rhombs. Ventral surface with three 



apertures. Stem com- 

 posed of several vertical 

 rows of plates. Cam- 

 brian ; Bohemia, Spain, 

 Northern France. 



Mitrocystites, Barr. 

 Like the preceding, ex- 

 cept that one side of the 

 calyx is composed of toler- 

 ably large, and the other 

 of small plates. Ordo- 

 vician ; Bohemia. 



Anomalocystites, Hall 

 (Aeteleocystites, Bill.) 

 Calycine plates smaller 

 and more numerous on 

 th *rl +- Vi 



tn6 convex sicie than 

 the COncave AnUS 





Pleurocystites squamosus, Billings. Ordovician ; Ottawa, Canada. 

 a, Calyx from the anterior side ; b, Same from the ^anal side ; c, Arms, 

 enlarged. Right and left reversed (after Billings). ' 



on 



, , , 



situated very low down 

 on the convex side. Arms feeble, filiform. Ordovician and Silurian ; North 

 America, England, Bohemia. 



Balanocystites, Dendrocystites, Barr. Ordovician ; Bohemia. 



Pleurocystites, Bill (Fig. 307). Convex side with large plates arranged 

 in cycles ; flattened side covered with very minute plates. Three isolated 

 pore-rhombs borne on the convex side. Arms two in number, robust. Stem 

 round, tapering distally to a point. Ordovician ; Canada. 



FIG. 308. 



Pseudocrinites quadrifasciatus, 

 Pearce. Silurian ; Tividale, Eng- 

 land. A, Calyx from one side. 

 B, Summit, showing mouth (m), anus 

 (a), and three of the arms. The 

 fourth arm (x) broken away, exposing 

 flattened surface of calyx. 



FIG. 309. 



Callocystites Jewetti, Hall. Silurian (Niagara Group) ; Lockport, 

 New York. A, Calyx from one side (natural size). JB, Ambulacral 

 grooves and three pectinated rhombs (rh), enlarged ; o, Mouth ; 

 an, Anus ; g, Genital pore (after Hall). 



Family 8. Callocystidae. Bernard. 



Calyx composed of large plates arranged in three or four cycles, and exhibiting 

 three to five pectinated rhombs, the component halves of which stand on contiguous plates, 



