180 BRITISH DESM1DJACEJE. 



Cells very small, about as long as broad or a little 

 longer, deeply constricted, sinus open and subrect- 

 angular ; semicells subelliptic, ventral margin very 

 strongly convex, apex slightly convex, or broadly 

 truncate and straight, lateral angles rounded or acutely 

 rounded. Side view of semicell circular. Vertical 

 view elliptic, poles often slightly pointed. Cell-wall 

 very finely granulate, granules arranged in regular 

 longitudinal and transverse series (about 9 longitudinal 

 and 5-6 transverse), the longitudinal sometimes more 

 distinct than the transverse series. Chloroplasts axile, 

 with one central pyrenoid. 



Zygospore unknown. 



Length 18-24^; breadth 15-23'5/i; breadth of 

 isthmus 5*7-9 n ; thickness 12-12-2 ^. 



ENGLAND. Enbridge Lake, Hants (Ron). Cornwall 

 (Bennett). 



SCOTLAND. --Near Heugh-head, Aboyne, Aberdeen 

 (Roy fy Bissett). 



Geogr. Distribution.- -Germany. Galicia in Austria. 

 Norway. Sweden. Bornholm. Denmark. Nova 

 Zembla. Siberia. Siam. Patagonia (var.). 



The degree of flattening of the apices of the semicells, and 

 also the precise disposition of the granules, is subject to 

 variation. In some forms the apices are almost straight, 

 whereas in others they are convex, although frequently 

 flattened in the middle. The vertical series of granules are 

 always strongly evident, hut the horizontal series are often 

 very indefinite. Considering these variations, we find it 

 impossible to regard either Borge's var. Schmidlei or Cos- 

 marium pseudorthopun'ctatum as forms worthy of separate 

 mention. 



172. Cosmarium synthlibomenum West. 

 (PL LXXXII, figs. 5-7.) 



Cosmarium synthlibomenum West, Alg. W. Ireland, 1892, p. 154, t. 21, 

 f. 11 [figures poor and not very accurate] ; Nordst. Index Desm. 1896, 

 p. 250; "West & G. S. West, Alg. N. Ireland, 1902, p. 42. 



Cells minute, about as Ions: as broad, moderately 



* <; c/ 



deeply constricted, sinus widely open with an obtuse 



