COSMARiUM. 97 



We had for some time regarded this Desmid as one of the 

 forms of C. Meneghinii , and shortly after Liitkemiiller's 

 description of the species we expressed this opinion in the 

 1 Journal of Botany/ xxxiii, 1895, p. 68. Since then, how- 

 ever, we have had reason to change this view. We find 

 C. difficile to be very widely distributed and remarkably con- 

 stant in its characters. It need never be confused with any 

 form of C. Menegliinii. The semicells have a characteristic 

 form, and the nature and disposition of the minute scrobicu- 

 lations give a very distinctive feature to the species. It 

 generally occurs in bogs, and most frequently among sub- 

 merged Sphagnum, in which situations C. Meneghinii is very 

 rarely found. Messrs. Roy and Bissett, and also Archer, must 

 have observed this Desmid many times in their examination 

 of Scottish and Irish Algaa, but doubtless included it in their 

 conception of C. Meneghinii. Similarly, there is every reason 

 to believe that the foreign distribution of C. Meneghinii 

 includes many records of G. difficile. 



The series of minute scrobiculations across the semicells 

 are of a similar nature to those on the cell-wall of C. zonatum 

 Lund, and C. binerve Lund. 



Var. sublseve Liitkem. (PL LXXIII, figs. 4, 5.) 



? Cosmarium Meneghinii Breb. forma rotundata Jacobs. Desni. Daneui. 

 1876, p. 198, t. 8, f. 20. 



C. difficile var. sublseve Liitkem. Desm. Attersees, 1893, p. 552, t. 8, f. 4 ; 

 West & G-. S. West, Alsf. S. England, 1897, p. 487 ; Schmidle, Lappmark 

 Susswasseralgen, 1898, p. 25; West & G-. S. West, Alga-fl. Yorks. 1900, 

 p. 93 ; Liitkem. Desm. Millstattersees, 1900, p. 8 ; West & G-. S. West, 

 Alg. N. Ireland, 1902, p. 35 ; Freshw. Alg. Orkneys and Shetlands, 1905, 

 p. 22 ; Further Contrib. Freshw. Plankton Scott. Lochs, 1905, p. 484 ; 

 Comp. Study Plankton Irish Lakes, 1906, p. 85. 



Semicells with a slightly more convex base and a 

 less prominently produced apex, upper (converging) 

 parts of lateral margins not retuse ; side view of semi- 

 cell sliofhtlv thicker : scrobiculations more numerous 



O t/ 



in the three transverse series ; cell-wall between the 

 scrobiculations smooth. 



Length 3 1-35 /A; breadth 20-22 5 p. ; breadth of 

 isthmus 5-6 /A; thickness 13-16 jn. 



ENGLAND. - - Cumberland ! Westmoreland ! Lanca- 

 shire ! "Wigton Moor, Cullingworth, Austwick Moss, 

 and Cocket Moss, W. Yorks ! Strensall and Pilmoor, 



VOL. III. ~ 



