BRITISH DESMIDIE^. 103 



differs from the inflation of Cosmarium omatum and C. commissurale, in 

 which plants it is longitudinal, and extends to or beyond the end margin. 



From all except Cosmarium Broomeii, this species is known by its qua- 

 drangular segments, the lateral margins of which are sloped, not rounded. 

 From that species it differs in its larger size, more distinct angles, and the 

 greater comparative length of the end margin, which is also convex and 

 sUghtly angular, whilst in C. Broomeii it is nearly straight. 



Length of frond -^^ of an inch ; breadth at constriction yttz '■> breadth of 

 segment ^. 



Tab. XVI. fig. 5. a. Sussex specimen ; b. empty frond of French specimen ; 

 c. end \dew. 



19. C. Broomeii (Thvvaites) ; segments compressed, minutely gra- 

 nulate, quadrilateral ; end view slightly inflated at the middle. 



Cosmarium Broomeii, Thwaites, in lit. cum specim. (1846). 

 In brackish water at Shirehampton near Bristol, Mr. Broome and Mr. 

 Thwaites. Piltdown, Sussex, Mr. Jenner. 



Frond as large as that of Cosmarium margaritiferum, deeply constricted at 

 the middle, the constriction forming a linear notch on each side. The seg- 

 ments are compressed, minutely granulate, quadrilateral, and twice as broad 

 as long ; the end margin is straight. 



The end view is twice as long as broad, slightly inflated at the middle and 

 broadly rounded at the ends. In the transverse view the inflation is greater, 

 and there is a slight constriction between it and the ends. 



Cosmarium Broomeii resembles in the front \iew some states of C. marga- 

 ritiferum, but differs in the end one. The inflation does not project at the 

 margin in the front view, as in C. omatum, and the lateral margms are less 

 rounded, the pearly granules are also smaller. 



Length of frond -g-i-g- of an inch ; greatest breadth g-i^ ; breadth at con- 

 striction XTV2 '■> tliickness at the inflation in end view g-L^ ; least thickness in 

 the end view yxry Diameter of sporangium -g-i-g-. 



Tab. XVI. fig. 6. a. frond with endochrome ; b. empty frond ; c. eud view; 

 d. transverse view. Tab. XXXII. fig. 7. sporangium. 



20. C. C(Blatum ; frond suborbicular ; segments crenate, rough 



with pearly granules ; end view slightly inflated at the middle. 



Near Machynlleth, North Wales, /. R. Tunbridge Wells and Ashdown 

 Forest, Sussex, Mr. Jenner. 

 Falaise, Brebisson. 



Frond nearly orbicidar, scarcely so large as that of Cosmarium margari- 

 tiferum, compressed, constricted at the middle, the constriction causing a 

 linear notch on each side. The segments are scolloped or broadly crenate : 

 each segment has six crenatures, four at the end, one at each side and one at 

 each iatermediate angle, the lateral ones being the largest, whilst between all the 



