AKTHRODESMUS. 107 



p. 260 ; W. & G. S. West, Further Contrib. Freshw. Plankton Scott. 



Lochs, 1905, p. 485; Borge, Beitrage, Alg. Schweden, 1906, p. 49 ; W. & 



G. S. West, Brit. Freshw. Phytoplaiikton, etc., 1909, p. 181 ; Phyto- 



plankton Engl. Lake Distr. 1909, p. 138 ; Hustedt, Desm. et Bacill. 



aus Tirol, 1911, p. 336. 

 Staurastrum convergens Menegh. Synops. Desm. 1S40, p. 228 ; Ralfs in 



Ann. Mag. Nat. Hist, xv, 1845, p. 158, t. J2, f. 1 ; Racib. Desm. Krakow, 



1884, p. 16 (sep.), t. 1, f. S. 



Scenodesmus convergens Kiitz. in Linnrea, xvii, 1843, p. 74. 

 Euastrum convergens Kiitz. Phycol. germ. 1845, p. 136. 

 Euastrum (Tttracantliium) convergens Nag. Gatt. einz. Alg. 1849, p. 114, 



t. 7, f. C 1. 



Cosmarium convergens De Bary, Coiij. 1858, p. 72. 

 Didymidium (Staurastrum) convergens A. ellipticum Reinsch, Algenfl. 



Frank. 1867, p. 154. 

 Staurastrum convergens a armigera Jacobs. Desm. Danem. 1876, p. 203 



[forma inflata et forma attenuator]. 



XanthuUum convergens Delp. Desm. subalp. 1S77, p. 76, t. 14, f. 13-23. 

 Arthrodesmus convergens a typica, /3 curta, et y minor Turn. Freshw. Alg. 



E. India, 1893, p. 134, t. 11, f. 32, 41, 42 ; t, 12, f. 3. 



Cells of medium size, about ly or 1^ times broader 

 than long (without the spines), very deeply constricted, 

 sinus opening widely outwards from a narrow and 

 sublinear extremity ; semicells more or less elliptic, 

 usually with one margin (and generally the dorsal 

 margin) slightly more convex than the other, lateral 

 ano-les sometimes rounded-conical, each normally 



O ^ 



furnished with a rather short and slightly incurved 



'-. 



spine. Vertical view rather narrowly elliptic, with 

 a short spine at each pole. Cell-wall smooth or 

 delicately punctate. Chloroplasts as a rule axile with 

 a single central pyrenoid in each semicell, but inclined 

 to be variable. 



Zygospore globose and smooth. 



Length 33 54/x; breadth without spines 40-04 /x, 

 with spines 50-90 p. ; length of spines 5*5-1 5 ft ; breadth 

 of isthmus 10-1 7 ji/,; thickness 18-26/x ; diam. zygosp. 

 39-48 p.. 



ENGLAND.- -Cumberland ! Westmoreland ! (Ralfo). 

 Lancashire! (Ralfs). AY., X., and E. Yorks! Cheshire 

 (Ralfs). Leicestershire (R <>//). Bucks! AYarwicks ! 

 Gloucester (Ralfs). Herts (Hassall). Surrey ! Sussex 

 (Ralfs). Kent (Ralfs). Hants! (Roy). Devon! 

 Cornwall! (Ralf*). 



WALES.- -Capel Curig (common in the plankton of 



