110 DESMIDS OF THE UNITED STATES. 



The ultimate subdivisions arc rounded and slightly emar- 

 ginate, each furnished with two spines usually divergently 

 curved. 



Diameter about 250 //. Frequent. 



This species is found in various form-, as illustrated by the 

 figures, and may be noted as 



Forma, GENUINA, (figs. 1,2). The typical plant. 



Forma, ni da, Wolle. (fig. 4). A form which occurs frequently 

 with almost all the subdivisions nude, devoid of spine-. 



Forma, elephanta, Wolle, (fig. 3). Of gigantic size, diameter 

 400 u. 



Mount Everett, Ma. 



Forma, apiculata, Menegh, (fig. 2). With series of minute 

 spines bordering the sinuses. 



Forma, simplex, Wolle, (fig. 8). Small, oval, subdivisions with 

 simply one small mucro. 



This may prove a distinct species ; the two specimens I had 

 from Florida were too imperfect from drying for satisfactory 



identification. 



M. BRACHYPTEBA, Lund. Plate XXXII. figs. 6, 7. 



About one-third longer than broad, elliptic, deeply con- 

 stricted in the middle; sinus an acute angle somewhat 

 ampliated ; semicells five lobed ; polar lobe longer than the 



intermediate lobes and separated from them by a wide -inns; 

 neck moderately distending to the dilated apes ; (neck tapering 

 towards the apex. Lund.), depressed centre forms a wide, 

 shallow notch. Intermediate and basal lobes short and nearly 

 equal in breadth; twice bisected; apices of lobules furnished 

 each with two rather long, somewhat curved .-pines; angles 

 and margins of the cud lube, and margins of the other lobes 

 also, provided with a few scattered -pine-. The figures of two 

 semicells -how considerable variation in the arrangement of 

 the spines and division- of lateral lobes. 



Diameter 140-150/'.., without spines; length 200-210 ,u. 



Collected near Minneapolis, Minn., by Miss E. Butler. 



