156 BRITISH DESMIDIACE^. 



the type ; lateral angles (or lobes) of semicells much 

 stouter ; central granules variable, sometimes as in the 

 type, but often reduced in number (with three large 

 central warts surrounded by one ring of 8 granules). 



Length 28-37 /u; breadth 31-43 /i; breadth of 

 isthmus 10*5-13 ^ ; thickness 22-26'5/x. 



SCOTLAND.- -Rhiconich, Sutherland ! 



IRELAND.- -Cromagloun and Glen Caragh, Kerry ! 



Geoc/r. Distribution.- -Brazil. Paraguay. 



153. Cosmarium dentiferum Corda. 

 (PL LXXVIII, figs. 17, 18.) 



Cosmarium dentiferum Corda in Almanacli de Carlsbad, 1840, p. 215, t. 6, 

 f. 41 ; Nordst. Borah. Desm. 1888, p. 192, t. 6, f. 4-5 ; Eoy &Biss. Scott. 

 Desm. 1894, p. 45; Nordst, Index Desm. 1896, p. 101. 



Cells fairly large, about as long as broad or very 

 slightly longer, deeply constricted, sinus narrow and 

 closed, with a widely dilated extremity ; semicells 

 reniform, with a slightly depressed (sometimes faintly 

 retuse) apex. Vertical view oblong, sides very slightly 

 convex, poles rounded. Cell-w^all granulate, granules 

 rounded, disposed in vertical and obliquely decus- 

 sating series, about 40 showing at the margin of the 

 semicell. 



Zygospore unknown. 



Length 92-104^; breadth 89-100 /u; breadth of 

 isthmus 28-37 JJL ; thickness 40 ^. 



ENGLAND.- -In Bracebridge Pool, Sutton Park, War- 

 wickshire ! 



SCOTLAND.- -Aberdeen and Kincardine ( Hoy fyBissett). 



Geoc/r. Distribution. --Germany. Bornholm. Iceland. 



This species is very closely allied to C. margaritatum and 

 C. conxprrsum (inclus. C. latum), only differing in the form of 

 the semicells. It is the greatly rounded superior angles 

 which cause the semicells to appear more or less reniform. 

 Messrs. Roy and Bissett state that it is very rare in Scotland, 



but that they had passed it over as a form of C. latum. 



' i 



