470 



NORTH AMERICAN INDEX FOSSILS. 



former and one of the latter. Ambulacra five, simple, or more 

 usually one or more of them branching once ; plates ornamented 

 with polygonal depressions, a more or less defined border and 

 granulose surface. (Type of genus.) 

 Rochester shale of New York. 



21. C. canadensis (Billings). (Fig. 1780.) Siluric. 



The two halves of each pectinate rhomb closely adjoin and are 

 not separated by a high wall as in C. jewetti. 



Rochester shale of New York and Ontario. 



XIII. Sph^rocystites Hall. 



Calyx spheroidal, wider than high, with 18 plates in four cycles 

 and a partial telescoping of the second and third cycles. Ambu- 

 lacra four, bifurcating many times. Pinnules widely separated, 

 slender, short, club-shaped. Pectinate rhombs three, one basal and 



Fig. 178 1. 



Spharocystites niultifasciatus, a large specimen, anal and top views. 

 (After Schuchert.) 



two Upper, with the two halves separated by an interval. Anal 

 area composed of a pyramid of six to eight pieces and an outer 

 circle of 10 to 14 pieces. Column stout, terminating basally in 

 a few '' roots." Siluric. 



22. S. multifasciatus Hall. (Fig. 1781.) Siluric. 



Base of calyx more or less excavated. Branches of ambulacra 

 varying from 14 to 2y, obscuring the suture lines. (Type of 

 genus.) 



Manlius of Maryland and West Virginia. 



