340 DESCRIPTION OF {Volygasirlca 



Yery like to Pyxidiciila gemmifer, of Virginia, but a larger and more 

 depressed fomi. It also approaches C. cingulatus. 



Coscr^oDiscrs Luna. — Disc covered with dense, punctate tubercles, 

 equal, radiant, but becoming, tov^ards the margin, loose and imequal. 

 It is nearest to C. ApoUinis. 



C. granulatus. — Small ; cells very small, giving a gi'anular appear- 

 ance to the disc ; dense, and disposed in rows ; eighteen to twenty- 

 one in 1-1 152nd. Diameter l-552nd. Fossil, Yirginia. 



C. spinulosus Testule flattened, surface finely porous ; margins 



of pores spinous; spines and pores about t^velve in 1-1 152nd. 

 Diameter l-576th. Fossil, Patagonia. 



C. mtmitus (Kiitz.)— Margin with dotted rays ; disc nearly smooth. 

 Diameter 1-1 41 6th. 



C. minor. — Margin smooth ; disc irregularly and densely punctato- 

 celhxlar. Diameter 1-1 150th to l-576th. Fossil in chalk marl, 

 Greece, Sicily, Peru, &c. Alive, Cuxhaven, 



C. striatus (Kiitz.) — Margin striated with radiating linos; disc 

 cellular; cells of centre without order. Diameter 1 -456th. Cuxhaven. 



C. cinctus. — The striae of the external rim radiating, but broken at 

 their middle ; central cells closely aggregated, those around loosely 

 so. Diameter 1 -324th. Alive, ^^haven. Fossil, Eichmond, Vir- 

 ginia. 



C. cruciatus = Pi/xidicula cmciata and Pgxidicula Selhnica (Ehr.) 

 — Cells hexagonal, arranged in straight, parallel lines, with a smooth 

 annular rim. 



Genus Ceaspedodiscts.— Shell composed of two equal orbicular 

 valves, not in chains ; surface cellular, cells having a radiating 

 arrangement ; otherwise not radiated nor divided by septa, but with 

 a sculptured tumid margin, of a different structure, and separable. 



Has the habit of Coscinodiscus, with an elegantly sculptured 

 margin (rim.) It differs from Coscinodiscus liiiilatus and similar 

 foi-ms, by its margin not becoming gradually lost in the disc, nor 

 being a mere boundary to it of the same structure ; but, on the con- 

 trary, separated from it by a distinct farrow, and having a different 

 structure. This border is cither developed at the first, or the being 

 exists primarily as a CcDiipylodiscas, the rim being a gradual 

 production. 



