110 BRITISH DESMIDIE^. 



Frond minute, smooth, two to three times longer than broad, slightly con- 

 stricted at the middle, attenuated and roimded at the ends. Endochrome in 

 three or four longitudinal fillets, which are interrupted at the suture. End 

 \iew circular, its endochrome with four geminate rays. 



This plant was placed in Penium by M. De Brebisson because its endochrome 

 is arranged in fillets, but in every other respect it agrees better with some of 

 the preceding species of this genus. It is more obtuse than the usual form of 

 Cosmarium attenuatum, but I have occasionally seen specimens of the latter 

 so nearly resembling the figure of C. curtum that I have doubted to which 

 species they belonged. It is much smaller than C. turgidum, and tapers more 

 than C Cucurbita and C. Thwaitesii. 



Length of frond ^^ of an inch ; greatest breadth yoVt- 



Tab. XXXII. fig. 9. a. mature frond ; b. empty frond ; c. end view of frond 

 with stellate endochrome. 



32. C. attenuatum (Breb.) ; frond fusiform, three or four times longer 

 than broad, slightly constricted at the middle ; transverse view 

 circular. 



Cosmarium attenuatum, Brebisson, in lit. cum icone (1846). 

 Near Bristol, Mr. Thwaites. Swansea, J. R. 

 Falaise, Bi'ebisson. 



Frond three or four times longer than broad, tapering, its ends obtuse ; end 

 view circular. The empty frond is finely punctate. 



Cosmarium attenuatum is much smaller and more tapering than C. tur- 

 gidum, and has less-rounded ends. Its fusiform frond distinguishes it from 

 C. Thwaitesii and C. Cucurbita. In general it tapers more than C. curtum, 

 but sometimes its ends are more obtuse, and then these species can only be 

 distinguished by the different arrangement of their endochromes. 



It is doubtful whether this plant and Cosmarium turgidum ought not to be 

 removed to Penium. 



Length of frond from ^-^o^ to ^^b" ^^ ^^ "^^^ 5 greatest breadth from j^^ 

 to YoV2^ ; breadth at constriction from ^-^^ to yq^q • 



Tab. XVII. a, b. fronds in usual state ; c. empty frond ; d. transverse view. 



33. C. turgidum (Breb.) ; frond oblong, punctate, constricted at the 

 middle and rounded at the ends ; transverse view circular. 



Cosmarium turgidum, Brebisson, in lit. cum icone (1846). 

 Henfield, Mr. Jenner. Swansea, J. R. 

 Falaise, Brebisson. 



Frond large, oblong, turgid, about three times as long as broad, distinctly 

 constricted at the middle and broadly rounded at the ends. Empty frond with 

 numerous, mmute, scattered puncta. 



Cosmarium turgidum differs from the allied species in its much greater size. 

 It is comparatively longer and more tapering than C. Cucurbita and C. 

 Thivaitesii, and its ends arc more rounded than those of C. attenuatum. 



