464 NORTH AMERICAN INDEX FOSSILS. 



a short distance. Column with alternately wide and narrow joints. 

 Pore-rhombs irregularly placed. (Type of genus.) 

 Trenton of Ontario and Quebec. 



10. G. logani Billings. Ordovicic. 



Summit abruptly truncated, base slightly rounded. Ambulacra! 



grooves extending only to the angles of the truncated apex and 

 each bearing at the end several long 

 pinnules bordered with side plates. 

 Each plate ornamented with three to 

 seven very much elevated, sharp ridges 

 which radiate from the center to 

 the sides ; spaces between the ridges 

 smooth. Small plates of column pen- 

 tagonal, their angles forming five spi- 

 ral lines around the column through- 

 out its length. Length one and one 

 fourth inches ; diameter two thirds 

 inch. 



Trenton of Quebec. 



VII. Caryocrinus Say. 

 Calyx ovoid or subglobose. Base 

 dicyclic, i. e., lowest plates (infra- 

 basals) four, unequal, followed by a 

 second row of six basals which alter- 

 nate in position with those of the pre- 

 ceding and succeeding cycles. Third 

 cycle consisting of eight plates of 

 which six are regarded as radials and 

 the others as interradials. Ventral 

 surface formed of six or more small 

 Fig. 1771. Caryocrinus orna. pigces. All plates of the calyx fur- 

 tus, with stem. (After Hall.) . , , . , . . <-, 



nished with pore-rhombs. Summit 

 plates without perforations. Mouth and ambulacral grooves situ- 

 ated below the ventral plates or tegmen. Anal opening protected by 

 a valvular pyramid and situated on the outer margin of the ventral 

 surface. Arms six to thirteen, situated on the ventral margin, and 

 relatively feeble. Stem long, composed of cylindrical joints. Siluric. 



