146 DESMIDS OF THE UNITED STATES. 



St. Donnellii, Wolle. Plate LXIII, fig. 20. 



Small, twice as long as wide, oblong-quadrate ; cytioderm 

 punctate and sulcate; semi-cells quadrangular with basal 

 angles rounded, sides crenulate; superior angles (four) pro- 

 duced into short, obtuse, diverging processes; end view 

 quadrangular. 

 Diameter 15 fi. 



Collected by J. Donnell Smith in Florida. 

 This species is nearest St. x)usillum, but unliiie it in the pro- 

 portionately longer cell, the almost smooth and sulcate mem- 

 brane, and the crenulate sides. 



St. incisum, Wolle. Plate LIT, figs. 12-14. 



Cytioderm granulate, margins serrately toothed; semi-cells 

 in front view cuneate, base broad, sides diverging to a con- 

 vex top; the upper portion on each side produced into short, 

 obtuse, tapering processes ; end view, five or six radiate ; 

 rays with broad base, somewhat tapering to the obtuse 

 apices ; sides serrately toothed ; the rays separated at their 

 broad base by an acnte-angled, or linear incision. 

 Diameter 36-40 pi. 



Principally from Splitrook and other ponds of New Jersey. 

 St. pulchrum and St. diatentwn have a leading feature of tliis 

 species— the incision, or notch between the bases of the rays, 

 but they are separated by the smooth membrane and differ- 

 ently formed notch. 



St. Mekiani, Eeinsch. Plate LVII, figs. 17-19. 



Cells in front view subrectangular, roughly granulate, 

 slightly constricted in the middle ; semi-cells somewhat en- 

 larged in the upper portion ; sometimes slightly constricted 

 near the end ; apex rounded; end view usually pentagonal, 

 but varies, more rarely, from four to six angular. 

 Diameter 1 6-24 /d. ; length about one-half more. 



Have found this species in various ponds of New Jersey 

 and Pennsylvania. 



St. Heleneanum, Wolle. Plate LV, figs. 6, 7. 



Small, finely granular; granules arranged in transverse 

 rows; semi-cells, front view, narrow, elliptic, ends slightly 

 emarginate; angles somewhat produced, and apices furcate; 

 \'ertical view triradiate, with large central inflation, rays 

 short, stout, tumid at base and furcate at apices; basal in- 

 flation furnished on each side with a small bicuspidate 

 prominence. 



Diameter 30-36 m. 



