13(3 DKSMIDS OF THE UNITED STATES. 



ST. TRIHEDRALE, Wolle. Plate LI, figs. 12, 13, 14. 



Small punctate-granulate; semi-cells, in front view and in 

 end view triangular, angles rounded, sides concave, sinus 

 narrow linear. 

 Diameter 30 //. 



Ponds, Mount Everett, Mass. 



This species, in front view, has the appearance of a (.'oma~ 

 rium near rctuKiim, Perty, and anymtatum, Xord., but the side 

 and end views are distinct. The seuii-cells are three sided, 

 pyramidal forms unlike those of a Coamarium. 



ST. TRIFIDUM, ISTord. Plate LI, figs. 28, 29. 



Cells about as broad as long, deeply constricted ; semi-cells 

 short cuneate, with ends dilated, and lightly retuse; superior 

 angles obtuse, trisected ; viewed from vertex triangular, 

 angles truncate, trifid ; sides somewhat concave; membrane 

 finely punctate. 



Diameter 30-50 //. Variable in size. 



Not frequent, but met with in localities widely separated, 

 Pennsylvania, New Jersey, and other States. 



ST. AVICULA, Breb. Plate LI, figs. 30, 31, 32. 



Semi-cells twice as broad as long, with a forked spine on 

 each side; each angle in end view terminated by a simple or 

 forked spine; cytioderm smooth. 



Diameter 25-30 >u., without the spines. 



Rather common species ; appears to be found frequently in 

 every State in which explorations are made. 



ST. COMMUTATUM, Kg. Plate LI, figs. 33, 34. 



Smooth or punctate-granulate; semi-cells diverging, ob- 

 verse semilunar; base broadly rounded, ends straight or 

 somewhat concave ; apices bifid ; end view triangular, angles 

 produced and apices bicuspidate; sides moderately retuse. 



Diameter 35-38 //. , omitting the spines. 



Ponds, Lehigh Valley, Pennsylvania. 



This form may not be strictly the plant described by the 

 author, Kutzing ; it is near it, and appears to stand between it 

 and A. Bulnheimianum, Rab. Have seen very few of them, 

 hence record the name merely provisionally. 



ST. BRACHIATUM, Ealfs. Plate LI, figs. 37, 38, 39 ; and Plate 



LXIII, figs. 29, 30, 31. 



Cells smooth; semi-cells with three diverging processes, 

 or according to other authors, 2-4-5 radiate, which are deeply 

 bifid or trifid at the apex; end view with three or four rays. 



