46 BRITISH DESMIDIACKJE. 



Zygospore unknown. 



Length 37 /^ ; breadth 22 ^ ; breadth of apex 15 '5 /* ; 

 breadth of isthmus 14 JJL ; thickness 15 p.. 



WALES.- -Bog above Capel Curig Lakes, Carnarvon- 

 shire ! 



SCOTLAND. Plankton of Loch nan Cuinne, Suther- 

 land (J. Murray) I Glen Nevis, Inverness! Poolewe, 

 Ross (Roy fy Bissett). 



Geogr. Distribution. Silesia in Austria. Poland. 



This species differs from C. decedens in its narrower apices, 

 the more rounded angles of the semicells, and in the dense 

 punctulation of the cell-wall. We have not seen the side 

 view of the type form, but, from Raciborski's description and 

 figures, one of its peculiarities seems to be the entire absence 

 of a constriction in this view of the cell. As a rule, the 

 presence or absence of punctulations cannot be considered in 

 the light of a specific character, but the punctulation of C. 

 tatricum is of such a peculiar nature that it furnishes a good 

 character for the easy recognition of the species. The punc- 

 tulations in this case are really minute scrobiculations or small 



/ 



cavities in the exterior of the cell-wall; they are exceedingly 

 dense, and give the entire cell-wall the appearance of being 

 minutely areolated. 



Var. novizelandicum Xordst. (PI. LXIX, figs. 11, 12.) 



Cosmarium tatricum var. novizelandicum Xordst. in Botan. Xotis. 1887, 

 p. 161 ; Freshw, Ala:. N. Zeal. 1888, p. 56, t. 6, f. 6; West, Alg. Engl. 

 Lake Distr. 1S92, p. 723. 



A larger variety with relatively longer cells, with 

 the basal angles of the semicells subrectangular ; cells 

 in side view with a slight but distinct constriction. 



Length 46-54 /x; breadth 25-36/1; breadth of apex 

 18-22 p; breadth of isthmus 14-20 /x; thickness 

 12-16 p.. 



ENGLAND.- -Kirk Fell, Cumberland ! 



WALKS. Llvn Bochlwvd, Carnarvonshire ! 



". ^ 



Geogr. Distribution.- -New Zealand. 



This variety is distinguished by the subrectangular basal 

 angles of the semicells and by the slight constriction in the 

 side view. 



