MARYLAND GEOLOGICAL SURVEY 503 



crowded arrangement of the granules and in the moniliform rows which 

 radiate from the center. A. ehrenhergii is very common in most of the 

 deposits, especially in the lower, where it occurs with large and bril- 

 liantly colored valves, while A. moniliformis is less common and not so 

 highly colored. The diameter of both is quite variable. 



Occurrence. — Calvert Formation. Flag Pond, f mile south of 

 Parker Creek, 3 miles north of Parker Creek, Plum Point, ^ mile north 

 of Forest Wharf, Nomini Bay, Chesapeake Beach, God's Grace Point, 

 Fairhaven, 1 mile west of Tracy Landing, 1^ miles southeast of Marriott 

 Hill, 1 mile north of Jewell, 1 mile north of Jones Point, 1 mile south 

 of Chesapeake E. K. Bridge, 1 mile northwest of West Eiver, 1 mile east 

 of Marriott Hill. 



Collection. — Maryland Geological Survey. 



Actinogyclus partitds (Grunow). 



Genus LIRADISCUS Greville. 



LiRADiscus ellipticus Greville. 



Genus STICTODISCUS Greville. 



Stictodiscus kittonianus Greville. 



Genus XANTHIOPYXIS Ehrenberg. 



Xanthiopyxis constricta Ehrenberg. 

 Xanthiopyxis globasa Ehrenberg. 

 Xanthiopyxis oblonga Ehrenberg. 



Genus COSCINODISCUS Ehrenberg, 



CosoiNODiscus APicuLATUS Ehrenberg. 



Plate CXXXIY, Fig. 13. 



Coscinodiscus apiculatus Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss., Berlin, p. 77. 

 Coscinodiscus apiculatus Ehrenberg, 1856, Mikrogeologie, pi. xviii, fig. 43. 

 Coscinodiscus apiculatus Schmidt, 1875, Atlas der Diatomaceen-kunde, pi. Ixiv, 



figs. .5-10. 

 Coscinodiscus apiculatus Rattray, 1890, Proc. Roy. Soc. Edinburgh, vol. xvi., p. 122. 



Description. — Valve circular, convex. Surface with markings angu- 

 lar and compressed over part of the valve and rounded and separated 

 over the other. Smaller toward the border. Central space minute. 



