BRITISH DESMIDIE^. 107 



26. C. orbiculatum (Ralfs) ; segments spherical, rough with pearly 

 granules. 



Cosmarmm orhicidahim, Ralfs, Ann. of Nat. Hist. v. 14. p. 392. t. 11. f. 2 

 (1844) ; Trans. ofBot. Soc. of Edinburgh, v. 2. p. 148. t. 16. Hass. Br. 

 Alg. p. 364. 



Dolgelley, /. R. Midhurst, Sussex, Mr. Jenner. Ambleside, "Westmore- 

 land, Mr. Sidebotham. 



Falaise, Brebisson. 



Frond minute, composed of two spherical segments, rough with pearly gra- 

 nules, giving a dentate appearance to their outlines, but wanting on the neck- 

 hke contraction between them. The transverse ^4ew has a large central 

 opening. 



Cosmarinm orbicidatum varies in size ; the larger specimens somewhat re- 

 semble the lateral view of Cosmarium margaritiferum ; the front view how- 

 ever of that species diifers in the shape of the segments and in the presence 

 of a Unear notch on each side at their junction. The granidated fronds distin- 

 guish it from the following species ; its central opening also is much larger. 



Length of frond from ^-ig- to j4-j of an inch ; greatest breadth from yiy to 

 yi-g- ; breadth at constriction y^Vo > diameter of sporangium -g-^-g ; length of 

 spme ^^oo- 



Tab. XVII. fig. 5. a. mature frond ; b. empty frond ; c. transverse view. 



Tab. XXXIII. fig. 9. sporangium. 



tt Frond smooth. 



27. C. moniliforme (Turp.) ; segments spherical, smooth. 



a. Segments united without the intervention of a neck. 

 /3. Segments united by a distinct neck. 



Tessarthronia tnoniliformis, Turp. Diet, des Sc. Nat. t. 7. f. 1.? (1820). 

 Tessarthra moniliformis, Ehr. Abh. d. Berl. Ak. 1835, p. 1/3 ; Tnfus. p. 145. 

 t. 10. f. 20. 



a. Dolgelley ; rare ; J. R. Charlton Fields near Manchester, Mr. Side- 

 botham. Ashdown Forest ; Fittleworth ; and Rackham Bogs near Pulborough, 

 Sussex, Mr. Jenner. 



/3. Penzance. 



Germany, Ehrenberg. 



The frond is small and quite smooth. In a. each segment is a perfect globe, 

 having a very small openmg through which it connects with its fellow. Their 

 appearance is one of mere juxtaposition, and their junction can only be ascer- 

 tained and the opening seen in a transverse view. This state is hable to be 

 mistaken for a not uncommon plant with two globular cells, which I consider 

 to belong properly to the Palmellese, and to be the Scenedesmus moniliformis 

 of Kutzing's ' Phycologia Germanica' and Brebisson's 'Alg. Fal.,' as also the 

 Trochiscia moniliformis of Meneghuii's ' Synopsis Desmidiearum.' The resem- 

 blance indeed is at times so complete that I have occasionally been puzzled to 

 distinguish them ; but m specimens of the latter some individuals may gene- 



