30 DESMIDS OF THE UNITED STATES. 



S. MONILIFORMK, Lund. Plate XL VII, fig. 11. 



Series of cells often long. firm, somewhat twisted ; usually 

 included in a mucous envelope. Cells average one-half 

 longer than broad, deeply constricted, sinus obtuse out- 

 wardly enlarged, back more or less produced ; seen from the 

 vertex triangular, sides somewhat retuse ; angles rounded, 

 isthmus sub- elongate, membrane smooth. 



Diameter about 20 //. 



Not infrequent in quiet waters, Florida ; less frequent in 

 Xew Jersey, Minnesota and Pennsylvania. 



S. EXCAVATUM, Ealfs. Plate IV, figs. 8, 9, 10-12. 



Cells twice as long as broad, with a deep, wide sinus on 

 each side, connected by two small sessile glands. 

 Diameter 9-12 //. 



Not infrequent in ponds ; sometimes it occurs with, and 

 sometimes without, the gelatinous sheath. 



S. VERTEBRATUM (Breb.), Ralfs. Plate IV, fig. 13. 



Cells about half as long as broad, with a deep narrow con- 

 striction, connected in the center by a simple, rather thick 

 gland ; more or less remote. Semi-cells narrow, elliptic, 

 smooth. Filaments twisted, usually surrounded by a mucous 

 sheath. 

 Diameter 12-14 yw. 



Rather rare ; the best specimens found were from Splitrock 

 Pond, Sussex Co., New Jersey. 



S. SERRATUM, Bailey. Plate IV, fig. 7. Plate XLIII, figs. 7, 8. 



Cells broader than long, deeply notched, or divided into 

 two transverse portions with acute, spiiielike projecting ends 

 which give a serrated outline to the chain. Cells closely 

 united by two short glandular processes. Usually sur- 

 rounded by a wide gelatinous sheath. 



Diameter 22-33 //.. including the projections. 



Prof. Bailey collected this species in South Carolina, Geor- 

 gia, and Florida, 1848 ; it is found frequently in New Jersey, 

 Pennsylvania and other Northern States. 



According to Wallich this species should be classed with 

 Onychonema, a new genus made by him to take in the forms 

 which have the glandular processes long. 



The glandular processes connecting the cells are sometimes 

 long, nearly equal to the length of a semi-cell ; in this condi- 

 tion it approaches very near to Onyckon< inn l< /r, Nord., a 

 Brazil form. The specimens vary considerably, but they do 



