122 DESMIDS OF THE UNITED STATES. 



view triangular with sides usually so sinuate as to produce a 

 three lobed appearance : each lobe terminated by a short 

 raucro. 



Diameter 45-48 //.. Smaller forms occur also. 



The cells of this species vary in size and somewhat in form 

 from elliptic to subreniform, turgid. 

 Neither very rare nor common. 



Yar. [NERME, Wille. Plate XL, figs. 3, 4. 



Somewhat larger than the true form, but otherwise reminds 

 one of it, notwithstanding the absence of the mucros. The 

 author of the name, adds, "semicells in vertical view trian- 

 gular, sides lightly retuse, angles unarmed." 

 Diameter 60 <>.. 



Northampton County, Pennsylvania. 



St. Dickiei, Ralfs. Plate XL, figs. 5, 6 ; and Plate LI, figs. 20, 21. 

 Semicel] smooth, snbelliptic, turgid ; spines short, curved 

 towards those of the other semicel] ; end view triangular, sides 

 sinuate, angle- mucronate. 

 Diameter 36-44 ;>.. 



Cells are about as long as broad ; semicells elliptic, but 

 having the outer margin more convex than the inner one ; 

 the mucros or spines, short, curved, and directed inwardly. 

 It occurs not infrequently in Pennsylvania, New Jersey, 

 Massachusetts, and probably in every State. 



St. aristiferum, Ralls. Plate XL, figs. 15, IB. 



Semicells smooth, triangular, constricted near the angles, 

 producing a mammillate appearance. Each angle furnished 

 with a long awn: end view with three, or rarely four awned 

 lobes. 



Diameter 15-20 //.. without the awns or spine.-, and with 

 them fully twice the size. 



Rather rare but it has been found in many States, from 

 Rhode Island, New Jersey, to Georgia. 



St. Lewisii, Wood. Plate XL, figs. 26, 27. 



Smooth, with a very ample sinus, obtuse -angled, which is 

 armed with a small -pine; semicells from the front broadly 



