62 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



Not Cymbella gastroides H. L. Smith, Type No. 118, which is C. mexicana A. S., 

 having a punctum in the middle of the central nodule; in outline it is like C. gastroides 

 var. minor Kuetz. 



Blue clay. 



PI. 18, Fig. 1 (an unusual form, but it resembles Grunow's. (Diat. Franz Jos. Land, 

 PL 1, Fig. 7.) 



CYMBELLA CYMBIFORMIS (KUETZ.) BREB. 



Valve cymbiform, slightly gibbous on the ventral margin; apices broad, somewhat 

 truncate; a punctum occurs on the ventral side of the median line; striae, 8 in 10 M, closely 

 punctate. 



Kirkwood Pond, N. J. 



PL 18, Fig. 2. 



CYMBELLA CISTULA (HEMPR.) KIRCHN. 



Valve cymbiform, with gibbous ventral margin and truncate apices; a distinct row of 

 several puncta occurs below the median line in typical forms. 

 Blue clay. 

 PL 18, Fig. 3. 



CYMBELLA LANCEOLATA (fiHR.) KIRCHN. 



Valve cymbiform, with gibbous ventral margin; apices truncate; axial area very nar- 

 row, scarcely widened in the middle; striae with fine close puncta. 

 Kirkwood Pond, N. J. 

 PL 18, Fig. 4. 



CYMBELLA MEXICANA (EHR.) A. S. 



Valve broad, with gibbous ventral margin and sub-rostrate, truncate apices; median 

 line with reflexed terminal fissures; striae with coarse puncta; a large punctum occurs in the 

 centre of the central area. 



Blue clay. 



PL 18, Fig. 5. 



CYMBELLA TUMIDA (BREB.) V. H. 



Valve cymbiform, with gibbous ventral margin and abruptly rostrate ends; median 

 line arcuate; axial area narrow; central area large, orbicular; below the central nodule is a 

 punctum; striae punctate. 



Crum Creek. 



PL 18, Fig. 7. 



SECTION 3. ENCYONEMA. FRUSTULES IN TUBES 



CYMBELLA VENTRICOSA KUETZ. 



Valve lunate, with straight or slightly gibbous ventral margin; axial area indistinct; 

 median line straight or nearly so; striae punctate. 



Very common, but extremely variable. The ventral margin is sometimes straight and 

 sometimes quite gibbous. 



PL 18, Figs. 14, 22; PL 38, Fig. 16; PL 40, Fig. 8. 



