34 DESMIDS OF THE UNITED STATE&. 



S. BRYOPHILA, (Breb.), Rab. (S. mnscicota, D. By.) Plate III. 



fig. 20. 



Cells cylindrical, two to four times as long as broad, ends 

 obtusely rounded, chloropbyl a single, broad, smoothly 

 defined, widely wound spiral band ; its revolutions one or 

 two. 

 Diameter 8 //. 



Dr. Wood reports this species, measure and form, from near 

 Philadelphia, growing among some mosses which were kept 

 constantly wet by overhanging dripping rocks. It formed 

 little transparent masses of almost colorless jelly, looking like 

 little drops of dew. 



Genus, PEXIUM, Breb, 



(Netrium, Xaeg. Cylindrocystis Menegh. ) 



Plate V, figs. 1-L> 



Cells straight cylindrical or fusiform, not incised nor constricted 

 in the middle ; ends more or less obtusely rounded. Chlorophyl 

 lamina axillary ; when seen transversely, radiately divergent, 

 arms often forked, and containing starch granules. 



Individuals swim free, scattered, or associated in gelatinous 

 masses ; cell membranes smooth or finely granulate, transparent 

 or fuscous, or reddish, often longitudinally striate. 



Multiplication takes place by divisiou r and by zygospores de- 

 veloped by the copulation of two cells. Comp. Introduction. 



P. DIGITUS, (Ehrb.), Breb. Plate Y, figs. 1, 2. Plate LXIV r 



fig. 1. 



Cells ovately cylindrical, or broadly elliptical, 3-5 times 

 longer than broad, each end subtruncately rounded, (Plate 

 LXIV, fig. 1). Chlorophyl lamina lobate in the periphery, 

 interrupted in the middle. Plate V, fig. 1, is a variety, 

 more elliptic than the typical form. Fig. 2 is a transverse 

 section. 



Diameter 60-80 >w. 



This species appears to be widely distributed from Maine to- 

 Florida and westward. Very variable in size and outline. 



P. LAMELLOSUM, Breb. Plate V, fig. 4. 



Cells oblong or fusiform cylindrical, often with a slight 

 depression in the middle, more or less attenuated towards the 



