338 DESCEIPTION OF [Poli/gastnca. 



CoscmoDiscvs Jfdvicans. — Small, with very smaU nou-radiaut cells, 

 yellow by transmitted, but white by reflected light. Peru and St. 

 Domingo. 



C. gigas. — Veiy large ; cells hexagonal radiant ; central ones the 

 smallest ; marginal very large ; rim striated. It is figured by Dr. 

 Bailey. Cells five to six in 1 -1200th near the margin. Fossil, 

 Yii-ginia. Alive at Ciixhaven. 



C. marginatus. — Cells of nearly uniform size, imperfectly radiant in 

 curved lines ; the rim furnished with radiating lines of smaller cells. 

 Cells nine to ten in l-1200th. Fossil in Vu-giuia. Alive at Cuxhaven. 



C. radiohtus. — Cells very small, equal, and radiant. Eighteen in 

 1-1 200th. Peru, Cuba, and Yirginia. 



C. suit His. — Similar to the last, but "^ath twenty-four cells in 

 1-1 200th; and of uniform size. 



C. apiculattis. — Cells slightly prominent and apiculate (pointed), 

 rendering the surface rough : disposed in the manner of rays ; ten 

 in 1-1 200th. Diameter 1 -324th. Vii'ginia. Has a general resem- 

 blance to Fyxidimda gemmifera. 



C. aster omphalus. — Cells larger, seven to eight in l-1200th, 

 rather prominent, and in rays, decreasing in size towards the 

 margin ; a eenti-al stellate umbilj^^is ; surface appearing as if over- 

 spread by a finely dotted membrane (veil.) Diameter 1 -324th. 

 Yirginia. 



C. centralis. — Differs by its smaller, equal, and radiating cells, 

 which are twelve in 1-1 200th; sui'face also not veiled. Has a 

 similar central stellate umbilicus. Yirginia and Sicily. 



C. velatus. — Differs from the preceding by wanting the centi-al 

 stellate umbilicus. Cells angular ; surface as if covered with a 

 gi-anular veil. Diameter 1 -492nd. 



C fimbriatus. — Cells small, thirteen to foiu-teen in l-1200th; im- 

 perfectly radiant and unequal ; near the margin occui-ring in lines, 

 and of smaller size. Diameter 1 -324th. Caltanisetta, Sicily. 



C. perforatus. — Cells small, evidently radiant, thirteen in l-1200th; 

 with a smooth central umbilicus, looking like a perforation ; margin 

 finely rayed. Diameter 1 -348th. Yirgioia. Allied to C.7?wJr?^^ws, 

 which, however, has not the smooth, central umbilicus. 



