THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 123 



NlTZSCHIELLA 

 NITZSCHIA LONGISSIMA (BREB.) RALFS 



Valve linear-lanceolate, with exceedingly long horns or beaks; keel puncta about 10 

 in 10 n; strise about 16 in 10 /j. L. to 500 ju. 



Shark River, N. J. 



PI. 33, Fig. 1. 



Forma parva V. H. Keel puncta, 10-12 in 10 /*. L. 70 /u. 



East Park Reservoir, Philadelphia. 



PI. 33, Fig. 10. 



Differs from N. closterium (Ehr.) Wm. Sin. in the keel puncta. 



The type form occurs in brackish and salt water. The occurrence of the variety in 

 fresh water is another instance of the finding of presumably brackish forms in the water 

 supply of the city. If these cases prove to be unusual, it may be because of one of two rea- 

 sons. The Schuylkill River, before the building of the dam at Fairmount, was tidal as far 

 as the Falls of Schuylkill, and brackish influences, while not now existent, may have caused 

 the growth of forms which now survive. Another reason may be that the opening of the 

 locks at Fairmount Dam may cause a slight admission of brackish forms from tidal water 

 below. The abundance of the brackish species appears to indicate that the first reason is 

 the more plausible. 



NITZSCHIA REVERSA WM. SM. 



Valve lanceolate, extended into beaks or horns curving in opposite directions; keel 

 puncta not evident; striae, "20-26" in 10 . L. 70 p.. 



Brackish water. Abundant in Duck Creek, Delaware River. 

 PI. 33, Fig. 11. 



NITZSCHIA ACICULARIS (KUETZ.) WM. SM. 



Valve lanceolate, with beaks or horns about half the length of the median part of the 

 valve; keel puncta, 18 in 10 p.; strise exceedingly delicate, "about 40 in 10 /u." L. 45 n. 

 Fresh water. Darby Creek. 

 PI. 33, Fig. 12. 



HOMCEOCLADIA AG. (1827) 

 (homoios, like, and clados, a branch) 

 Frustules like Nitzschia, but enclosed in branching or simple tubes. 



HOMCEOCLADIA FILIFORMIS WM. SM. 



Frustule linear, tumid in the middle, obtuse at the ends ; valve linear-lanceolate, with 

 somewhat acute apices; keel central or nearly so; keel puncta, 8 in 10 /*; striae delicate. L. 



108 M- 



Fresh and brackish water. Newark, N. J. 

 PI. 33, Fig. 15. 



