140 DESMIDS OF THE UNITED STATES. 



acute granules; end view triangular, angles truncate, or 

 drawn out into short, stout processes, ends tipped with 

 small spines. Zygospores orbicular, armed with elongated 

 spines forked at the ends. 

 Diameter 25-30 //. 



Frequent in ponds and small pools. 



ST. CREXULATUM, Naeg., (Delp.). Plate LIII, figs. 26-29. 



In front view hardly separable from the preceding; end 

 view with four, five or six angles, each produced into a short, 

 stout, somewhat tapering ray; ends tipped with short spines r 

 which are sometimes merely rudimentary. 

 Diameter 30-38 yu. 



Frequent in ponds, ditches and the like. 



Some authors unite these forms with the preceding species; 

 others hold them as distinct for the reason that the rays often 

 have transverse series of large granules, which give a crenulate 

 appearance to the margins. Our artist failed to bring out this 

 feature as distinctly as it should be. 



ST. MURICATUM, Breb. Plate LIII, figs. 3-6. 



Suborbicular, deeply constricted, sinus narrow linear, or 

 slightly enlarged outwardly; rough with somewhat conical 

 granules ; semi-cells subsemiorbicular, angles obtusely 

 rounded, or truncate; end view triangular, sides convex, 

 angles rounded or truncate spinous. 

 Diameter 40-45 pi. 



Pools and ditches in many distantly separated localities, 

 . but not very numerous. 



ST. ASPERUM, Breb. Plate LIII, figs. 7, 8. 



In comparison with the preceding (St. muricatum), gran- 

 ules are emarginate, or divided ; semi-cells broadly elliptic ; 

 sinus much wider, and sides in end view straight ; otherwise 

 very near it. 



Habitat and size the same. 



ST. RUGULOSUM, Breb. Plate LII, figs. 41, 42. 



Semi-cells elliptic, denticulate at their sides; end view 

 triangular, with angles broadly rounded and sides slightly 

 concave or straight. 

 Diameter about 38 p. 



Very nearly related to the preceding ; I quote the diagnosis 

 of the author. Bailey reports it from New York and Rhode 

 Island ; I add it from Pennsylvania and New Jersey. Not a 

 rare form. 



