108 BRITISH DESMIDIEiE. 



» 



rally be perceived which have a slight interval between the globes, whilst its 

 solitary globes are filled with endochrome. In Cosmariiim moniliforme, as 

 the globes are united they are in close contact, and when separated their con- 

 tents escape at the orifice. 



Both Kiitzing and Meneghini refer to the Tessarthra moniliformis as iden- 

 tical with the plant described by them under the names mentioned above, but 

 I have no hesitation m considering that it is the present plant. Ehrenberg's 

 figure, which exhibits a frond dividing and forming two smaller globes between 

 the original ones, appears to me decisive of the question. M. De BreTaisson 

 concurs in this opinion, that the Tessarthra moniliformis, Ehr., is not the 

 Trochiscia moniliformis of Meneghini's ' Synopsis.' 



The var. /3. resembles more nearly the form of Cosmarium orbiculatum, 

 from ha^nng, like that species, a distinct connecting neck ; but its fronds are 

 quite smooth and without granules or puncta. 



Length of frond -^^y ^^ ^^ "^^^^^ 5 greatest breadth ^^^3^ ; breadth at con- 

 striction -2tVo • 



Tab. XVII. fig. 6. a. usual state ; b. variety /3 ; c, d. dividing fronds ; 

 €. empty frond ; /. transverse view. 



28. C. connatum (Breb.) ; segments punctate, each about two-thirds 

 of a circle, uniting by their plane surfaces ; end view circular. 



Cosmarium connatum, Breb. in lit. {cum icone) (1846). ■ 



Ambleside, Westmoreland, Mr. Sidebotham. Dolgelley, /. R. 

 Falaise, Brebisson. 



This is one of the largest species in the genus. The fronds are nearly twice 

 as long as broad, and slightly constricted at the middle. In the front view 

 the segments are broader than long ; one-third of the margin is interrupted by 

 their broad junction, and the remainder constitutes two-thirds of a circle ; a 

 distinct border is always present, and often appears striated. 



The empty frond is punctate rather than granulate, and the end view is 

 circular. 



With a little attention this species is easily recognized. Its very broad 

 junction without lateral incisions distinguishes it from those species which have 

 compressed fronds, and its large size and segments broader than long from 

 those which have a circular end view. Its aspect in the front \'iew is more 

 like that of Staurastrum tumidum, but the latter has more elliptic segments, 

 and generally shows one at least of its nipple-like angles. 



Length of frond -^^ of an inch ; greatest breadth yy xr 5 breadth at con- 

 striction y^Vq* 



Tab. XVII. fig. 10. a. mature frond; b. empty frond. 



29. C. Cucurbita (Breb.) ; frond punctate, slightly constricted at the 

 middle and rounded at the ends ; transverse view circular. 



Cosmarium Cucurbita, Breb. in Desm. Alg. No. 1103 (184 ). Ralfs, Annals 

 of Nat. Hist. V. 14. p. 305. t. 1 1. f.' 10 ; Tra7ts. nfBot. Soc. of Edinb. 



