148 DESMIDS OF THE UNITED STATES. 



serrate. Reinsch's figures indicate an absolutely smooth 

 membrane, and in his description he writes membrana glabra. 

 Satisfied I have Reinsch's prototype in size, and detail of 

 construction, it is but just to retain the name given by him. 

 The plants generally recorded for pseudofurdgerum would 

 probably be better placed with St. eustephanum. 



St. cuneatum, Wblle. Plate XLVIII, figs. 7, 8. 



As long as wide, divided by a deep constrictioD into two 

 broadly cuneate semicells ; base convex, broad ; sides, each with 

 three to six sharp teeth, converge from the base to a concave- 

 truncate end ; superior angle- somewhat produced, making a 

 short process, apex bifid or trifid : end view triangular, sides 

 -lightly convex, angles bisected ; on the top six processes 

 radiating from the centre and extending to, or slightly over 

 the margin-. 



I >iameter I 1- hi //. 



Ponds, Pennsylvania. 



In front view, this form bears much similarity to a plant 

 found on the Island of Spitzbergen ami named St. megalonotum, 



Nonl., hut in end view it is entirely distinct. 



St. spongiosum, Breb. Plate XLVII, figs. 5-8. 



Thickly covered with short spines which are forked at the 

 apex : semicells semiorbicular, spinulose ; end view triangular, 



angles rounded ; sides -lightly convex and bordered with 

 forked spines or -lent processes. 

 Diameter 45-50 ". 



This specie- appears to be sparsely but widely distributed. 

 The specimen- vary considerably in different localities; figs. 

 7,8, represent the more frequent form ; Naegeli Bupposed it to 

 be a new species and named it St. Griffitheanum. 



St. arctiscox, Ehrb. Plate XLVII, 6gs. '., in. 



('ells about one-fourth longer than broad, moderately con- 

 stricted, sinuses obtuse angled ; semicells subglobose, slightly 

 depressed, furnished in the middle with (usually) nine straight 

 divergent processes ; above these, another whorl consisting, 

 usually, of six similar, but shorter processes, apices trifid. 

 Membrane punctate. 



Diameter 100-120 u. 



