MARYLAND GEOLOGICAL SURVEY 



505 



CosciNODiscus EXCENTRicus Ehrenberg. 

 CosciNODiscus ELEGANS Greville. 



CosciNODiscus EXCAVATUS VAR. GENNINA GrunOW. 



CosciNODiscus GAZELLAE Janisch. 

 CosciNODiscus GiGAS Ehrenberg. 

 CosciNODiscus GRANDIVEUS Schmiclt. 

 CosciNODiscus HETEROMORPHUS Schmidt. 



CosciNODiscus HETEROPORUS Ehrenberg. 

 Plate CXXXIV, Fig. 15. 



Coscinodiscus heieroporus Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss., Berlin, 



p. 365. 

 Coscinodiscus heteroporus Schmidt, 1875, Atlas der Diatomaceen-kunde, pi. Ixi, 



fig. 4. 

 Cosci7iodiscus heteroporus Rattray, 1890, Proc. Roy. Soc. Edinburgh, Tol. xvi, p. 92. 



Description. — Yalve circular, with striated border. Markings hex- 

 agonal, increasing towards the semi-radins where they are about 2 in .01 

 mm., and then decreasing towards the border to G in .01 mm. " Diam. 

 .072 to .112 mm." Differs from G. hullieus which, as Rattray remarks, 

 is " sometimes confounded " within its larger size and the more uneven 

 distribution of the lager cells near the semi-radius. 



Occurrence. — Calvert Formation. 1 mile east of Marriott Hill, 

 1 mile northeast of West River, 1 mile north of Jones Point. 



CoUection. — Maryland Geological Survey. 



Coscinodiscus lewisianus Greville. 

 Plate CXXXIV, Fig. 16. 



Cosci7iodiscus lewisianus Gre^iUe, 1866, Trans. Roy. Mic. Soc. London, vol. xiv, p. 



78, pi. viii, tigs. 8-10. 

 Coscinodiscus lewisianus Schmidt, 1875, Atlas der Diatomaceen-kunde pi. Ixvi, fig. 13. 

 Coscinodiscus lewisiamis Rattray, 1890, Proc. Roy. Soc. Edinburgh, vol. xvi, p. 150. 



Description. — Valve elliptical, occasionally rhombic-elliptical. Mark- 

 ings, 3 in .01 mm. at center, irregular, or when central space is present 

 somewhat radiating and becoming more or less parallel to major axis. 

 Border sharply defined, usually broad, with oblique striae 8 to 10 in 

 .01 mm. Diam. .072 to .087 mm. 



A form at Wildwood, Xew Jersey, shows produced ends. In the Hun- 

 garian deposits the central dots are more evident. Found also at Moron, 

 Spain, California, and Trinidad. 



