6TAHRA8TRUM. 133 



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

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

 Diameter 16-24 //.; length about one-half more. 



Have found this species in various ponds of New Jersey 

 and Pennsylvania. 



St. Hf.lexkam m, Wolle. Plate XLIY. figs. 6 3 7. 



Small, finely granular ; granules arranged in transverse 

 rows; semicells, fronl view, narrow, elliptic, ends slightly 

 emarginate; angles somewhat produced, and apices furcate; 

 vertical view triradiate, with large central inflation, rays short, 

 stout, tumid at base and furcate at apices; basal inflation fur- 

 nished "ii each side with a small bicuspidate prominence. 



Diameter 30- 36 -. 



Frequent in Splitrock pond, N< u Jer 



There i> a trace of similarity between thi- desmid and 

 St. vestitum, Elalfs, but, while the latter baa two or more 

 .-lender forked spines in the middle of each side, mine has 

 stouter forked prominences on the inflated base of each ray: 

 the Bides, moreover, are nol concave, but undulate convi 

 size of plant much smaller. 



St. cerastes, Lund. Plate XLIII, figs. ( i. 7. 



Rather broader than long ; semicells in front view, ends 



lunate, drawn oul in the middle of tin ocave side into a 



subcorneal column ; the lateral horns arc robust, short, incurved, 

 apices obtuse ; the exterior margin coarsely granulate and often 

 very rough with large emarginate, bifid, verrucae ; the interior 

 margin nude; end view quadrangular, angles produced into 

 stout, straight horns, apices tridentate; margins and areas 

 * variously roughened, with larger and -mailer granules and 

 often dentate with large conical, or emarginate-bifid verrucae. 

 Diameter (i(i-7< //.. 



Not abundant, nevertheless a cosmopolite. 

 The figures represent a smoother specimen. 



St. gracile, Ralfs. Plate XLIII, figs. 16, 17. 



Semicells rough, elongated on each side into a slender pro- 

 cess which is terminated by minute spines; end view triradiate. 

 Diameter 40-50 u.\ length about one- third this measure. 



Ponds, pools, ditches from Vermont to Florida, and west- 

 ward as far as explorations have been made. 



