STAURASTRUM. 147 



Frequent in Splitrock Pond, New Jersey. 



There is a trace of similarity between tliis desmid and St. 

 vestitum, Ealfs, but, while the latter has two or more slender 

 forked spines in the middle of each side, mine has stouter 

 forked prominences on the inflated base of each ray; the 

 sides, moreover, are not concave, but undulate convex ; size 

 of plant much smaller. 



St. Cerastes, Lund. Plate LIV, figs. 6, 7. 



Rather broader than long ; semi-cells in front view, ends 

 lunate, drawn out in the middle of the concave side into a 

 subconical column ; the lateral horns are robust, short, in- 

 curved, apices obtuse ; the exterior margin coarsely granu- 

 late 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 

 smaller granules and often dentate with large conical, or 

 emarginate-bifid verrucae. 

 Diameter 60-70 /^. 



Not abundant, nevertheless a cosmopolite. 

 The figures represent a smoother specimen. 



St. gracilb, Ealfs. Plate LIV, figs. 16, 17. 



Semi-cells rough, elongated on each side into a slender 

 process which is terminated by minute spines ; end view 

 triradiate. 

 Diameter 40-50 yu. ; length about one-third this measure. 

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

 ward as far as explorations have been made. 



St. Ophiura, Lund. Plate LIV, figs. 10, 11. 



Large, slightly constricted in the middle; semi-cells some- 

 what obovate, end convex and ornate with bifid papillae ; 

 -superior angles produced laterally with elongated, thin, 

 almost colorless, straight, or lightly incurved rays, with 

 margins more or less denticulate, and apices dentate. 

 Viewed from the vertex seven (rarely six or eight) rayed ; 

 rays attenuated, long, apices tridentate, margins serrate- 

 dentate; center ornate with a crown composed of seven 

 (rarely six or eight) four-parted papillae. 

 Diameter 140-150 M- 1 length 65-80 m- 



More abundant in the waters of New Jersey than of Penn- 

 sylvania ; found specimens also in ponds, Massachusetts. 



