488 SYSTEMATIC PALEONTOLOGY 



margin. Furrows broad; their outer margins enclosing an elliptical 

 space half as broad as the valve." Cleve, 1894. 



This Diploneis, originally named RJiapidodiscus because when found 

 it had been accidentally enclosed, as was proved later, in the rim 

 of a Melosira, is of interest by reason of its orbicular form, although 

 otherwise naviculoid. The Naviculeae appear to be introduced in the 

 Miocene deposits by this genus, several forms of which are rather com- 

 mon, while Navicula proper is scarcely seen until a later period. 



Occurrence. — Calvert Formation. Plum Point, Cambridge Well 

 (rare). 



Collection. — Maryland Geological Survey. 



Diploneis crabro var. limitana Schmidt. 

 Diploneis didyma (Ehrenberg). 

 Diploneis prisca Schmidt. 



Genus PINNULARIA Ehrenberg. 

 Pinnularia peregrina Ehrenberg. 

 Genus PLEUROSIGMA Wm. Smith. 

 Pleurosigma normanii Wm. Smith. 

 Pleurosigma normanii var. marylandica (Grunow). 



Tribe PSEUDO-RAPHIDIE/^. 



Family FRAGILLARIE/E. 



Genus DIMEROGRAMMA Ralfs. 

 DiMEROGRAMMA POSSILE GrunoW. 



DiMEROGRAMMA PULVUM (Gregory). 

 DiMEROGRAMMA NOVAE-CAESARAE Kain and Schiiltzc. 



Genus RHAPHONEIS Ehrenberg. 



Ehaphoneis gemmifera Ehrenberg. 



Plate CXXXV, Fig. 11. 



Ehaphoneis gemmifera Ehrenberg, 1844, Monatsb. d. k. Akad. d. Wiss., Berlin, p. 87. 

 Ehaphoneis gemmifera Van Heurck, 1881, Syn. Diat. Belg., pi. xxxvi, tig. 31. 



Description. — Valve rhombic-lanceolate, with large, rounded granules 

 in longitudinal rows. L. of v. .095 mm. 



