134 DESMIDS OF THE UNITED STATES. 



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



Large, slightly constricted in the middle; semicells 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 -i\ or eight) rayed ; rays attenuated, long, 

 apices tridentate, margins serrate-dentate ; centre ornate with a 

 crown composed of seven (rarely -i\ or eight) four-parted 

 papillae. 



Diameter 140-1 oil //.; length 65-80 n. 



Mure abundant in the waters of New Jersey, than of 

 Pennsylvania; found specimens also in ponds, Massachusetts. 



Yar. TETRACERUM, Wolle. Plate XLI Y, tig-. 1, 2. 



Yar. PENTACERUM, Wolle. Plate KLIV, fig. 3. 



The one four-armed, and the other live-armed ; the crown 

 papillae correspond in number with the arms; in other details 



they are not unlike the typical form ; the serrate-dentate mar- 

 gins vary greatly in different specimens. 



These varieties I collected only in Denmark pond, Passaic 

 County, N. J., where they occurred frequently. 



St. macrocerum, Wolle. Plate KLIII, figs. ';, 1, 5. 



Very large, granularly rough ; semicells, front view, sub- 



cuneate, truncate base and rounded top; upper angles 

 laterally produced into long, slightly tapering, straight or 

 lightly incurved arms, margins serrate, end- bifid ; end view 

 six radiate. . 



Separated from the preceding partly by the less number of 

 arms, the less, central elevation (front view) and the absence of 

 the crown of papilla?. 



Diameter 150-180 ,". 



Not rare in New Jersey waters. 



St. odontatim, Wolle. Plate KLIII, figs. 8, 9. 



Of equal length and breadth ; semicells in front view sub- 

 quadrangular, end convex, upper angles drawn out laterally 

 into straight or lightly incurved arm-, as long as the breadth 

 of the body of the cell; margins serrate, apices furcate; the 



