COSMAETUM. 87 



1:1-6. Cell-wall smooth. Chloroplasts axile, with a 

 central pyrenoid. 



Zygospore unknown. 



Length 24-36 p. ; breadth 19-20 p.; breadth of isth- 

 mus 5-9 p. ; thickness 10-14 p.. 



ENGLAND. Westmoreland ! Lancashire ! W., N., and 

 E. Yorks ! Essex ! Cambridge ! Middlesex ! Surrey ! 

 Hants! (Rot/). Devon! Cornwall! 



WALES. Llyn Idwal, Carnarvonshire ! 



SCOTLAND.- -General, but scarce! (Roy fy Bissett). 

 Common in Sutherland and the Outer Hebrides ! 



IRELAND. Donegal ! Galway ! Kerry ! Londonderry ! 



O t/- t/ / 



Ram s Island, Louo'li Xeao-h ! 



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Geofjr. Distribution.- -France. Germany. Switzer- 

 land. Bohemia and Galicia in Austria. Denmark. 

 Finland. Faeroes. Greenland. Bosnia. Siberia. Japan. 

 India. New Zealand. Australia. W. and E. Africa. 

 Azores. United States. Brazil. Argentina. Patagonia. 



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This species lias been largely confused with C. Menegliinii 



Breb., with which it is connected by certain intermediate 



/ 



forms. In its typical condition, wliicli is also its commonest 

 state, it is very distinct, and the form of the semicells at once 

 distinguishes it from Brebisson's species. Moreover,, it 

 retains its characters so constantly in all parts of the world, 

 and is so widely distributed, that there are no preponderating* 

 reasons why it should be regarded as a variety of C. 

 Meneghinii. The eight equal and pronounced undulations at 

 the margin of each semicell render C. impreasulum easy of 

 recognition. The hollow between the two apical undulations 

 is often less deep than the remaining hollows, giving the 

 appearance of a decided apical region of the semicell. 



C. impressulnm should be compared with C. undulatum, 

 from which it differs in its general proportions, in the form 

 of its semicells, and in the fewer marginal undulations. 



Borge (' Siissw. Chlor. Archang.' 1894, p. 27, t. 2, f. 27) 

 has described a Desmid from X. Eussia as C. suHmpressulum. 

 AVe have also recorded the same form from the United 

 States (consult West & G-. S. West, ' Some N. Amer. Desm/ 

 1896, p. 247, t. 15, f. 18). It appears to differ from C. 

 irnpressulum in the rectangular basal part of the semicells, in 

 the more crenate sides, in the prominent apex, and in the 

 broad inflation 011 each side of the vertical view. 



