98 BRITISH DESMIDIE.E. 



ttt Frond with pearly granules which give a denticulate appearance 



to the margin. 



11. C. tetraophthalmum (Kiitz.) ; frond deeply constricted at the mid- 

 dle ; segments semiorbicular, rough with pearly granules which 

 give a crenate appearance to the margin. 



Heterocarpella tetrophthalma, Kiitzing, Synop. Diatom, in Linncea 1833, 



p. 597. f. 87. Brebisson, Alg. Fal. p. 56. t. 7. 

 Cosmarium ovale, Jenner, FL of Tunhridge Wells, p. 196 (1845). 

 Euastrnm tetrophthalmum, Kiitz. Phy. Germ. p. 136 (1845). 

 Cosmarium tetraophthalmum, Brebisson in lit. (1846) ; not of Meneghini 



according to Brebisson. 



Probably common. Penzance ; Dolgelley ; and near Carmarthen, J. R. 

 Sussex ; Hants ; and Surrey, Mr. Jeyiner. Near Bristol, Mr. Thwaites. Near 

 Ambleside, Westmoreland, Mr. Sidebotham. Aberdeen, Mr. P. Grant. 



Germany, Kiitzing. Falaise, Brebisson. 



Frond compressed, longer than broad, larger than that of Cosmarium 

 margaritiferum, and deeply constricted at the middle, thus acquiring a linear 

 notch on each side. The segments are semiorbicular, or more usually two- 

 thirds of a circle. The pearly granules, by their roundness, produce at the 

 margin a crenate rather than a dentate appearance. The transverse view is 

 broadly elliptic. 



Cosmarium tetraophthalmum may be distinguished from C. Ralfsii and C. 

 pyramidatum by its dentated margin, and from C. ovale by its differently- 

 shaped frond and its scattered granules. The pearly granules are, in their 

 form, unlike those of C. Brebissonii. It is a larger plant than C. margariti- 

 ferum, and has also a more rounded margin. 



Its sporangia have been gathered by Mr. Thwaites ; they are large and 

 their spines finally branched. 



Length of frond -^\-^ of an inch ; breadth of segment 3^ ; thickness in side 

 view 4-|-g ; diameter of sporangium -^\-g ; length of spines of sporangium 2TT2 • 



Tab. XVII. fig. 11. a. front view of mature frond; b. empty frond; 

 c. transverse view. Tab. XXXIII. fig. 8. sporangium with empty fronds 

 attached. 



12. C. ovale (Ralfs) ; frond elliptic, deeply constricted at the middle ; 

 segments with a marginal band of pearly granules, the disc punctate. 



Euastrum, No. 6, Bailey, Amer. Bacil. in Amer. Journ. of Science and Arts, 



V. 41. p. 295. f 28. 

 Cosmarium ovale, Ralfs, in Annals of Nat. Hist. v. 14. p. 394. t. 11. f. /. 



d, e. (1844); Trans, of Bot. Soc. of Edinburgh, v. 2. p. 15. t. 16. 



Hassail, Brit. Algce, p. 366. 

 Euastrum carinatum, Ehr. (Professor Bailey in lit. 1846). 



"Weston Bogs near Southampton, Mr. Jenner. Ambleside, Westmoreland, 

 Mr. Sidebotham. 



West Point, New York, Bailey. Falaise, Brebisson, 



