THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 49 



SYNEDRA PULCHELLA VAR. FLEXELLA N. VAR. 



Frustule slightly attenuated at the ends, truncate, somewhat tumid in the middle and 

 flexed. Valve lanceolate, with obtuse or subcapitate apices and with two almost imper- 

 ceptible constrictions at the middle producing a tumid appearance; pseudoraphe distinct; 

 pseudo-nodule absent. L. 56 ^; striae, 14-16 in 10 p.. 



Some valves are bent and incised on one side. The outline of the valve is that of 

 pulchella. 



Common at Newtown Square. 



PI. 12, Fig. 2. 



SYNEDRA RADIANS KUETZ. 



Frustules linear, in small fasciae. Valve 34 n in length, linear, with apices rostrate, 

 obtuse, sometimes slightly capitate; pseudoraphe distinct; striae about 20 in 10 n. 



Fresh water. 



PL 10, Figs. 32 and 33. 



There is difficulty in recognizing S. radians K. as described and figured by different 

 authors. On Plate 12, Fig. 8, I have drawn a specimen from H. L. Smith's Type Slide 

 No. 574, labelled S. radians Kuetz., not Wm. Smith, which, however, corresponds closely 

 to Smith's figure (Brit. Diat. 1,P1. 11, Fig. 89). De Toni gives S. radians Kuetz. as equivalent 

 to S. tenera Wm. Sm. Van Heurck's figure of S. radians, and also the figure of ulna var., 

 said to be synonymous with H. L. Smith's S. radians, which does not correspond to the 

 specimens on Smith's slide in my possession, are confusing. In Van Heurck's Synopsis the 

 striae are said to be 16 or 17, while De Toni describes them as subtle and from 17 to 24 in 

 10 ju. The length is quite variable. 



Several species of Synedra resemble S. radians in the mode of growth, as they are 

 adnate at first, in short bands, the frustules being sessile on other plants or objects, attached 

 at the terminal nodules which, although scarcely visible in most forms, are probably pres- 

 ent in all. The frustules are not closely connected at the free end, and soon become en- 

 tirely detached. 



In Diatoma and Fragilaria, we find a punctum or pore at one end of a valve, but not 

 in line with the pseudoraphe; in Synedra, a minute pore is usually found in the position of 

 the terminal nodule and, in some species, indications of a central nodule are observed; the 

 median line is wider but there is no raphe. In the fresh-water Synedrae, many of which 

 are among the longest of diatoms, living in running streams, the terminal nodules are much 

 more indistinct, while the marine forms have distinct terminal nodules, are not, as a rule, 

 found in bands, and assume a more naviculoid outline. 



SYNEDRA VAUCHERLE VAR. PARVULA (KUETZ.) RAB. 



Valve lanceolate, with produced or rostrate apices; pseudo-nodule wide, excentric. L. 



17 M . 



Cram Creek. 

 PI. 12, Fig. 5. 



Fig. 6 represents a variety with coarser striae from the Schuylkill River. Both are 

 easily mistaken for Fragilaria intermedia. 



