192 BRITISH DESMIDIACE^. 



Geogr. Distribution. Germany. Gralicia in Austria. 

 United States. 



We have regarded the var. podolicum as constituted by 

 those forms of C. Turpinii which possess a few emarginate 

 crenations on each side just below the apex of the semicell, 

 and a series of large granules on each side of the isthmus. 

 The granulation of the apex appears to be very variable, and 

 the granules in various parts of the cell are often geminate. 

 The binate central tumour is exactly typical. The smallest 

 forms are those recorded by Johnson from the United States. 

 Schmidle observed the zygospore at Heidelberg. 



Var. eximium var. nov. (PL LXXXIII, fig. 3.) 



A rather small variety with more decidedly pro- 

 jecting apices ; semicells with a crenate margin just 

 under the apices, with a single central tumour, the 

 granules of which are arranged in two concentric 

 series around three central ones, and with a single 

 large granule on each side of the isthmus. 



Length 62 ^ ; breadth 54 /A; breadth of isthmus 17 p. ; 

 thickness 31 /n. 



IEELAND.- -Near Westport, Mayo ! 



This variety is nearest to C. Turpinii var. duplo-minus 

 Schmidle ('Lappmark Siisswasseralgen/ 1898, p. 39, t. 2, f. 4), 

 but is larger, with differently crenated lateral margins, a 

 smaller apex, more numerous granules, and a more granulated 

 central tumour. It agrees with var. duplo-minus in the 

 possession of the large granule on each side of the isthmus. 



179. Cosmarium didymoprotupsum sp. nov. 



(PI. LXXXVIII, fig. 8.) 



Cells of medium size, a little longer than broad, 

 very deeply constricted, sinus narrowly linear with a 

 dilated extremity ; semicells broadly truncate-pyrami- 

 date, basal angles broadly rounded and granulate, sides 

 convex, in the upper part with about 4 emarginate 

 crenations, upper angles scarcely rounded, apex trun- 

 cate and straight. 5 G-sranulate : cell-wall within the 



i * O 



