118 BRITISH DESMIDIE.E. 



1. A. convergens (Ehr.) ; segments elliptic, each having its spines 

 curved towards those of the other. 



Arthrodesmus convergens, Ehr. Infus. p. 152. t. 10. f. 18 (1838). Hassall, 



Brit. Algce, p. 357. 

 Staurastrum convergens, Meneghini, Synop.Desmid. inLinncea 1840, p. 228. 



Ralfs, in Annals of Nat. Hist. v. 15. p. 158. t. 12. f. 1 ; Trans, of Bot. 



Soc. of Edinburgh, v. 2. p. 145. t. 15. Brebisson, in lit. 

 Euastrum, No. 12, Bailey, in Amer. Joxirn. of Science and Arts, v. 41. p. 296. 



t. 1. f. 11 (1841). 

 Euastrum convergens, KUtzing, Phy. Germ. p. 136 (1845). 



Dolgelley and Penzance, /. R. Sussex and Kent, Mr. Jenner. Herts, 

 Mr. Hassall. Yate near Bristol, Mr. Broome. Aberdeenshire, Dr. Dickie 

 and iifr. P. Grant. Kerry, Mr. Andreios. Near Congleton, Cheshire ; and 

 Ambleside, Westmoreland, 3Ir. Sidebotham. Rochdale, 3Ir. Coates. 



Germany, Ehrenherg, K'dtzing. Falaise, Brebisson. West Point, New 

 York, Bailey. 



Frond smooth and deeply constricted at the middle ; the transversely 

 elliptic segments have on each side a curved spine which converges with the 

 similar one of the other segment. 



The frond has a gelatinous covering, which is sometimes distinctly seen, 

 sometimes imperceptible. 



Arthrodesmus convergens differs from A. Incus by its larger size and elliptic 

 segments. 



Length of frond from ^-i-g to -g^ of an inch ; breadth, not including spines, 



from g-L- to j^y ; including spines, from 3J j to 3-!^ ; breadth at constriction 

 1 



2 36 8* 



Tab. XX. fig. 3. a. frond with endochrome ; b. empty frond ; c. end view ; 

 d. frond dividing. 



2. A. Incus (Breb.) ; segments with end margin truncate. 



a. Segments externally lunate ; spines diverging. 

 /8. Segments gibbous on each side near the base ; spines of the 

 one segment parallel to or converging with those of the other. 



Cosmarium Incus, Brebisson (1839), according to Meneghini in Synop. 



Desmid. 

 Staurastrum Incus, Meneghini, Synojo. Desmid. in Linncea 1840, p. 228. 



Ralfs, in Annals of Nat. Hist. v. 15. p. 158. t. 12. f. 2 ; Trans, of Bot. 



Soc. of Edinburgh, v. 2. p. 145. t. 15. 

 Euastrvm, Bailey, iti Amer. Jotirn. of Science and Arts, v. 41. t. 1. f. 12? 



(1841). 

 Euastrum retusum, KUtzing, Phy. Germ. p. 136 (1845), (according to 



KUtzing in lit. cum icone). 

 Arthrodesmus Incus, Hassall, Brit. Freshwater Algce, p. 357 (1845). 



Dolgelley and Penzance, J. R. Weston Bogs near Southampton ; and 

 several stations in Sussex, Mr. Jenner. Yate near Bristol, Mr. Broome. 

 Aberdeenshire, Mr. P. Grant and Dr. Dickie. Near Ambleside, Westmore- 

 land, Mr. Sidebothatn. 



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



