122 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



SPECTABILES 

 NITZSCHIA SPECTABILIS VAR. AMERICANA GRTJN. 



Frustule linear, slightly constricted in the middle, with sub-cuneate ends; valve linear, 

 slightly arcuate, tapering to the sub-rostrate ends; keel excentric, keel puncta sometimes 

 confluent, 4-6 in 10 p, prolonged into short costse; striae distinct, 14 in the middle, 18 at the 

 ends in 10 n (but variable in different specimens). L. 186 M- 



Blue clay, especially at Tioga St. 



PI. 33, Fig. 3; PI. 39, Fig. 1. 



This is, probably, one of the most beautiful of the Nitzschise. It sometimes, according 

 to De Toni, reaches a length of 520 ju. 



Grunow states that his variety is found in the S. Bridgeton deposit. In a slide of 

 Mceller labelled "Bridgeton, Maine," I find specimens identical in every respect with the 

 Philadelphia form. 



LINEARES 

 NITZSCHIA LINEARIS (AG.) WM. SM. 



Valve linear, slightly inflexed in the middle; keel excentric; keel puncta, 8-9 in 10 M, 

 the two median distant; striae about 30 in 10 ju. Frustules in zone view narrowed toward 

 the ends, truncate. L. 75 M- 



Very common in fresh water. 



PI. 32, Fig. 18. Fig. 20, PI. 40, a transverse section of frustule. 



LANCEOLATE: 



NITZSCHIA PALEA (KUETZ.) WM. SM. 



Valve linear-lanceolate, slightly rostrate at the apices; keel puncta, 10 in 10 p., the 

 median not distant; striae, 33-36 in 10 /*; zone view linear, with rounded ends. L. 25-65 p.. 

 Fresh water. 

 PL 32, Fig. 15. 



NITZSCHIA AMPHIBIA GRTJN. 



Valve lanceolate, apices sometimes slightly produced, rounded; keel puncta, 8-9 in 

 10 M; striae, 16 in 10 /i. L. 20-32 ju. 

 Fresh water. 

 PL 32, Figs. 14 and 25. 



NITZSCHIA COMMUNIS RAB. 



Frustule linear, slightly attenuated at the obtuse ends; valve elliptical-lanceolate, 

 attenuated toward the obtuse ends; keel puncta, 12 in 10 ju; striae more than 30 in 10 p. 

 L. 35 ji. 



Fresh water. 



PL 32, Fig. 19. 



NITZSCHIA INTERMEDIA HANTZSCH 



Valve linear-lanceolate; keel puncta, 8 in 10 n; strise about 24 in 10 M- L- 100 ju. 

 Crum Creek. Not common. 

 PL 33, Fig. 2. 



