CLASS II CYSTOIDEA 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, 
tapering distally 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, reeumbent 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. 
1 Hybocystites, Wetherby. Ordovician. 
Family 9. Agelacrinidae. Hall. 
Calyx composed of a large number of small, irregularly arranged plates, and 
either furnished with a short stem, or fixed by a broad base. Plates pierced by pores, 
usually united in pairs. Mouth central; anus eccentric, provided with valvular 
pyramid. Arms placed in radial grooves on eaterior 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 

Fic. 310. 
Agelacrinus Cincinnatiensis, Roemer. Fic. 311 
Ordovician ; Cincinnati, Ohio. Indi- 1G: : 
vidual of the natural size adherent to Asteroblastus stellatus, FEichwald. Ordovician ; 
shell of Strophomena alternata. 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, and protected by covering plates ; the 
latter are furnished with articular facets for the attachment of pinnules, and 
* 
