THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 111 



EPITHEMIA BREB. (isss) 

 (epithema, a cover or lid) 



Frustules epiphytic, solitary, sometimes geminate, adherent on the ventral side at the 

 ends; in zone view rectangular, sometimes tumid in the middle. Valve arcuate, having an 

 interior costate stratum or transverse septa extending to the girdle, often detached, and 

 an exterior valve surface with transverse rows of puncta. Central and terminal nodules 

 not easily seen; in some species a true raphe is indicated. 



The resemblance between Epithemia and Eunotia has been already mentioned. In 

 the shape and striation of the valves there is an approach to Cymbella. 



The genus is divided into two groups, one in which the costse alternate with double 

 rows of puncta, as in E. turgida, and the other in which the rows of puncta are more than two. 



The endochrome usually consists of a band lying along the ventral zone and extending 

 in two flaps on the valves. 



EPITHEMIA TURGIDA (EHR.) KTJETZ. 



Valve arcuate, with ends subcapitate ; costse radiate, 4 in 10 p, alternating with double 

 rows of puncta. Median nodule central, the raphe curved toward the ventral edge which 

 it closely follows. 



Parasitic on algse. Very common in fresh water, especially in ponds. In the figure 

 the valve is asymmetrical with respect to the transverse axis, an unusual condition. 



PL 31, Fig. 14. 



EPITHEMIA ARGUS KUETZ. 



Valve with dorsal margin convex, and ventral margin nearly straight; ends rounded, 

 constricted; costse robust, alternating with more than two rows of puncta; zone view rec- 

 tangular, the thickened ends of the costse forming large nodules in a row along the edge of 

 the valve next to the connecting zone. 



Cystopleura argus (Ehr.) Kunze. 



Common in fresh water. 



PL 31, Figs. 15 and 21. 



EPITHEMIA ARGUS VAR. ? 



Valve strongly arcuate on the dorsal side and concave on the ventral ; tapering to the 

 rounded but not produced ends; costae at unequal distances, about 2 in 10 n; granules in 

 transverse rows, 8 in 10 /u. L. 100 p. 



Pensauken, N. J., artesian well. 



PL 31, Fig. 16. 



EPITHEMTA MUELLERI A. S. ? 



Valve broad, convex, slightly arcuate, with obtuse, somewhat constricted apices; 

 costse about 4 in 10 ju; striae, 12-14 in 10 M; in zone view the outline is rectangular, slightly 

 tumid in the middle. L. 78 ju. 



Blue clay. 



PL 31, Fig. 17. 



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