70 DESMIDS OF THE UNITED STATES. 



Pennsylvania, New Jersey, not frequent, but turns up 

 every now and then, sometimes in considerable numbers. 



In size, form, and arrangement of chlorophyl, this species 

 is often a good representative of C. Candianum, Delp. 



C. PACHYDEBMUM, Lund. Plate XV, figs. 2, 3. 



Cells 1;;-1 \ times longer than broad ; sinus narrow linear ; 

 semicells with straight base, rounded angles ; sides rise nearly 

 at right angles and then converge, forminga high arch ; they 

 contain two chlorophyl masses; viewed from the vertex, oval ; 

 isthmus wide, cytiodenn firm, distinctly punctate. 

 Diameter 75104 I ,". 



Had specimens from Budd'e Lake, New Jersey ; from Ne- 

 braska Notch, Vermont, collected by C. G. Pringle ; and 

 from Mt. Everett, Massachusetts. 



This species is separated from ( '. Ralfsii by its usually greater 

 proportionate length, firmer eytioderm, ami wider isthmus. 



C. GAiiERiTUM, Nord. Plate XVI, figs. 16, 17. 1*. 



Cells Blightly longer than wide, with narrow isthmus, deep 

 constriction and narrow, -lightly gaping sinus; semicells 

 triangular with straight, <r somewhat reniform base, rounded 

 lower angles, convergent, straight, >r Blightly convex sides! 

 ends more or less truncate ; membrane smooth ; end view oval! 

 Bide view circular. 

 Diameter 40-55 n. 



Springs and ponds, Pennsylvania and New Jersey. 



Fig. 47 represents a small form found in a pond on Mt. 

 Everett, Mass., measures only 29 u. diameter. The smaller 

 size, straight sides, and more broadly truncate ends may prove 

 it to be a different species. I note it provisionally a variety 

 of the typical plant. 



C. polymazum, Nord. Plate XVI, figs. 38-40. 



( 'ells about as long as wide, deeply constricted ; sinus narrow 

 linear, widening somewhat outwardly; semicells subelliptic, 

 margins with about sixteen crenae, and within the margin- a 

 concentric series of granules t<> correspond ; area smooth with 

 six papillae arranged in the form of a triangle, three in the 

 first row nearest the margin, then two, then one; seen from 

 the vertex, elliptical, truncate at ends, with a papilla at each 

 angle and from these two longitudinal series of granules ; 



