THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 61 



CYMBELLA AFFINIS KUETZ. 



Valve about three times as long as broad, strongly convex on the dorsal side and 

 straight on the ventral; apices sub-rostrate; striae punctate; axial area narrow, not widened 

 in the middle; median line curved; a small or indistinct punctum on the ventral side of the 

 median line (not shown in the figure). 



Common in ponds. Abundant in East Park Reservoir. 



PI. 18, Fig. 18. 



CYMBELLA EXCISA (KUETZ.) DE TONI 



Valve as in affinis, but with tumid and excised ventral margin ; a punctum is found on 

 the ventral side (not shown in the figure). 



According to Cleve this is a variety of C. affinis. 

 Common in ponds. 

 PL 18, Figs. 15, 19 ? 



CYMBELLA PAKVA (WM. SM.) CL. 



Valve semi-lanceolate, with produced apices; ventral margin slightly tumid; axial 

 area narrow; striae coarsely but obscurely punctate. 



C. affinis and C. parva are quite variable, the latter differing by its lanceolate form 

 and the absence of a punctum, which, however, is sometimes difficult to recognize. In a 

 gathering of C. parva, it is quite possible to find numerous abnormal forms which appear to 

 be sporangial, so that specific distinctions are difficult if based on occasional specimens. 



Common in ponds. 



PL 38, Fig. 14. 



CYMBELLA AMPHICEPHALA N^EGELI 



Valve unequally elliptical, with broad, rostrate apices; axial area narrow; median line 

 straight; central area small, rounded; striae, 12 in 10 M on the dorsal, closer on the ventral, 

 side and at the ends. 



Kirkwood Pond, N. J. 



PL 18, Fig. 16. 



CYMBELLA SINUATA GREG. 



Valve linear-elliptical, gibbous on the ventral side; axial area indistinct; central area 

 widened on the ventral side nearly to the margin. 

 Crum Creek. 

 PL 18, Fig. 13. 



SECTION 2. COCCONEMA. FRUSTULES STIPITATE 



CYMBELLA ASPERA (EHR.) CL. 



Valve large, cymbiform, arcuate on the dorsal, slightly gibbous on the ventral side; 

 axial area linear, broad, slightly widened in the middle; no row of puncta on the ventral 

 side. The puncta form curved longitudinal lines and the innermost row on the ventral 

 side appears sometimes distant from the others, but not as in C. cistula. 



Cocconema asperum Ehr. 



Cymbella gastroides Kuetz. 



