190 BRITISH DESMIDIEiE. 



1. S. quadricauda (Turp.) ; cells generally four, oblong, rounded at 

 their ends, disposed in a single row; each extremity of the two 

 external ones usually terminated by a bristle. 



Achnanthes quadricauda, Turpin, Diet, des Sc, Nat. par Lew. Atl. Veg. ves. 



f. 8 (1820) ; Mem. du Mus. f. 6. 

 Scenedesmus magnus et S. longus, Meyexi, Nov. Act. Acad. Nat. Cur. v. 14. t.43. 



f. 26-29 (1828). Kiitzing, Sijnop. Diatom, in Linncea 1833, p. G06. 

 Scenedesmus quadricaudatus a. cornutus, Ehr. Abh. d. BerJ. Ak. 1833, p. 309. 



Ralfs, Annals of Nat. Hist. v. 15. p. 402. t. 12. f. 4 ; Trans, of Bot. 



Soc. of Edinburgh, v. 2. p. 159. t. 15. Hassall, Brit. Freshwater Algce, 



p. 393. 

 Scenedesmus quadricauda, Brebisson, Alg. Fal. p. (iQ (1835). Meuegh. 



Synop. Desmid. in Linncea 1840, p. 206. 

 Sce?iedesmus caudatus, Corda, Aim. de Carlsb. 1835, p. 123. t. 4. f. 50. 



Kutzing, Phj. Germ. p. 139. 

 Arthrodesmus quadricaudatus, Ehr. Infus. p. 150. t. 10. f. 16 (1838). Bailey, 



Amer. Journ. of Science and Arts, v. 41. p. 292. t. 1. f. 17. 



yS. External cells with three bristles. 



y. ecornis (Ehr.) ; all the cells similar, and without bristles. 



Achnanthes quadrijuga, Turpin, Diet, des Sc. Nat. f. 5 (1820). 

 Scenedesmus Leibleinii, Kiitz. Leib. Bot. Zeit. 1830, f. 3; Synop. Diatom. 



p. 607. Meuegh. Synop. Desmid. p. 207. 

 Scenedesmus quadricaudatus fi. ecornis, Ehr. Abh. d. Berl. Ak. 1833, p. 309. 



Commou. Wales and Cornwall, J. R. Sussex ; Kent ; and near South- 

 ampton, Mr. Jenner. Bristol, Mr. Thioaites and Mr. Broome. Herts, Mr. 

 Hassall. Ayrshire, Rev. D. Landsborough. Aberdeenshire and Banffshire, 

 Mr. P. Grant. Northamptonshire, Rev. M. J. Berkeley. Kerry, Mr. An- 

 drews. Manchester, Mr. Williamson. Ambleside, Mr. Sidebotham. Roch- 

 dale, Mr. Coates. 



Germany, Kiitzing, Ehrenberg, &c. Falaise, Brebisson. Maine to Vir- 

 ginia, and hi Mississippi River, Bailey. 



Frond composed of from four to eight oblong cells, which are generally 

 larger than those of any other species in the genus, about three times as long 

 as broad, and rounded at their ends ; the external cells are usually the most 

 turgid, and their bristles are directed outwards. 



The colouring matter is pale, with minute scattered granules. 



In /3. the cells are smaller, and the external ones, besides the usual terminal 

 bristles, have another from the centre of the outer margin. 



The variety y. is described by some authors as a distinct species ; but I agree 

 with Ehrenberg in considering it a state of ^S". quadricauda, from which it differs 

 only in having no bristles. 



Length of cell y^Vr ^^ ^^^ ^^^^^^ '■> breadth ■^-^. 



Tab. XXXI. fig. 12. a, b, e, d. fronds with endochrome ; e,f. emj)ty fronds ; 

 g. variety (3; h. variety y ; i. dividing frond of y. 



