ECHINODERMA TA—CYSTOIDEA . 



469 



19. P. clarki Schuchert. (Fig. 1778.) Siluric. 



Elongate in outline. Ambulacra extending to the column. Each 

 ambulacrum with about 44 pinnules. 



Manlius of West Virginia. 



XII. Callocystites Hall. 



Calyx ovoid, composed of 25 plates arranged in four cycles, 

 with a partial telescoping of the second and third cycles. Pectinate 



Fig. 1779. Callocystites jewetti, with 

 enlargement of ambulacra and rhombs. 

 (After Hall.) 



Fig. 1780. Callocystites canadensis. 

 (After Schuchert.) 



rhombs three, one basal and two upper, component halves on 

 bordering plates and usually separated by an interval, and gen- 

 erally surrounded by an elevated margin. Mouth slit-like and 

 forming center of radiation for the arms. Ambulacra five, slightly 

 excavated, sometimes bifurcating. Stem well developed, tapering 

 distally to a point. Siluric. 



20. C. jewetti Hall. (Fig. 1779.) Siluric. 



Each rhomb surrounded by a high wall. Anal opening between 



second and third cycles of plates, excavated in two plates of the 



