142 DESMIDS OF THE TTNITED STATES. 



Diameter in front view, including arms, 50-58 /A ; thick- 

 ness of body 20-25 //. 



The front presentation, not unlike other forms, but the 

 vertical and lateral views are quite distinct in the usual in- 

 flation of the body. 



The name indicates the habitat. 



ST. ALTERNANS, Breb. Plate LII, figs. 26-28. 



Semi-cells granulate, elliptic or oblong, two or three times 

 as long as wide, and from their twisted position, unequal in 

 front view ; end view with three obtuse and rounded angles, 

 forming short rays, alternating with those of the other semi- 

 cell. 



Diameter 20-28 //. Frequent. 



ST. DILATATUM, Ehrb. Plate LXIII, figs. 32, 33. 



Small, granulate ; semi-cells fusiform, equal ; end view 

 with three, four or five short, broad, truncate rays, granules 

 arranged in transverse lines. 



Diameter 40 //. Frequent. 



Distinguished from the preceding, mainly, by the semi-cell& 

 not being twisted. 



ST. SILATATUM, Nord. Plate LTII, figs. 22, 23. 



Cells in front view fully twice as wide as long, deeply con- 

 stricted ; sinus with rounded base, outwardly enlarged ; 

 semi-cells sublanceolate, ends straight, lightly undulate ; 

 end view five lobed, margins smooth. 

 Diameter 30 yu. ; length 13-16 //. 

 Ponds, Florida. 



ST. CYRTOCERUM, Breb. Plate LIII, figs. 30, 31. 



Cells rough with minute granules ; semi-cells, front view r 

 subcuneate, top broadly convex, superior angles produced 

 into short, stout, curved processes; end view triangular; 

 each angle produced into a curved horn-like process with 

 end toothed or divided; granules arranged in transverse 

 lines. Semi-cells often so twisted as to make one-half appear 

 longer than the other half. 



Diameter 35-40 //. 



Var. MAJOR, Wolle. Plate LIV, figs. 1, 2. 



Not unlike the typical form except in size ; often attains 

 to a diameter 120 /*. 



