CLASS IF 



CVSTOIDKA 



187 





and are separated by an interval. Mouth slit-like, and forming the centre of radia- 

 tion for two to five pinnulate arms which are protected by covering pieces, and either 

 repose upon the calyx, or are sunk below the surface in grooves. Stem well developed, 

 taperiii'/ <H*t<iUij to a point. Ordovician and Silurian. 



Pseudocrinites, Pearce (Fig. 308). Calyx ovate, two- to four-sided, and 

 composed of four cycles of polygonal plates. Anus closed by valvular 

 pyramid, and occupying a lateral position. Pore-rhombs three in number ; 

 one placed above the base, the remaining two to the right and left of the 

 anus. Arms two to four, recumbent upon the calyx, extending to the base, 

 and beset with biserial jointed pinnules. Stem robust. Silurian; England. 



Lepadocrinus, Hall ; Apiocystites, Forbes. Silurian. 



Callocystites, Hall (Fig. 309). Calyx with four pore-rhombs. Arms some- 

 times bifurcating. Silurian ; North America. 



? Hybocystites, Wetherby. Ordovician. 



Family 9. Agelacrinidae. Hall. 



Calyx composed of a large number of small, irregularly arranged plates, and 

 > if It <r furnished with a short stem, or fixed by a broad base. Plates pierced by pores, 

 a finally united in pairs. Mouth central; anus eccentric, provided with valvular 

 jiii rn mid. Arms placed in radial grooves on exterior of the calyx, and protected by 

 covering plates. Ordovician to Carboniferous. 



Agelacrinus, Vanuxem (Fig. 310). Calyx in the form of a depressed or 

 convex disk, stemless, and attached by the entire under surface ; composed of 

 numerous, small, polygonal, usually imbricating plates, which are perforated 



Fin. 310. 



Agelucrinus Cincinnatiensis, Roeinfir. 

 Ordovician; Cincinnati, Ohio. Indi- 

 vidual of the natural size adherent to 

 shell of Strophomena alternata. 



FIG. 311. 



Asteroblastus stellatus, Eichwald. Ordovician 

 Pulkowa, Russia. Natural size (after Schmidt). 



by fine, and, for the most part, conjugate pores. Mouth surrounded by four 

 oral plates ; radiating from this are five small, more or less curved arms, 

 which are embedded in grooves on the outer surface, and are protected by a 

 double row of covering plates. Ordovician ; North America and Bohemia. 

 Rare in Silurian, Devonian, and Carboniferous. 



Sub -genera: Lepidodiscus, Hemicystites, Cytaster, Hall; Edrioaster, Billings. 

 Ordovician; North America. 



Mesites, Hoffmann. Globose, with truncate base, probably pedunculate. 

 Calyx plates small, polygonal, and exhibiting conjugate pores. Arms five, 

 very small, embedded in radial grooves, arid protected by covering plates ; the 

 latter are furnished with articular facets for the attachment of pinnules, and 



