ARTHRODESMUS. 113 



clear proof that ^1. Lapczynskii Gutw. is merely typical A. 

 octocornis, Gutwinski having fallen into the error so repeatedly 

 made in dealing with Desmids of regarding certain of the 

 mucous rods connected with the pores in the cell-wall as an 

 armature of small spines. 



Messrs. Roy and Bissett have recorded from Scotland 

 (from a pool on Cnlblean, beside the old road from Tarland 

 to Ballater, Aberdeen) the Desmid described by Jacobsen 

 ( l Desin. Danem/ 1876, p. 211, t. 8, f. 28) as Xanthidium 

 octocorne forma IMPAR. We have not seen this Desmid and 

 are very doubtful concerning its inclusion under Arthro- 

 desmus octocornis, as it seems to agree more closely with forms 

 of Xanthidium Smith-it. Jacobsen/s description and figure 

 are insufficient to determine this point. The lower angles of 

 the semicells possess one long spine and the upper angles two 

 long spines. We give a copy of Jacobsen's figure (PL CXVII, 

 % 21). 



11. Arthrodesmus bifidus Breb. 



(PL CXVII, figs. 11-13.) ' 



Arthrodesmus bifidus Breb. Liste Desm. 1856, p. 135, t. 1, f. 19 ; Arcli. in 

 Pritch. Infus. 1861, p. 736 ; Rabeiih. Flor. Europ. Alg. Ill, 1868, p. 226 ; 

 Liind. Desm. Suec. 1871, p. 55; Boldt, Sibir. Chlorophy. 1885, p. 109; 

 Cooke, Brit. Desm. 1887, p. 137, t. 48, f. 2 [figures erroneous" ; De 

 Toni, Syll. Alg. 1889, p. 1064 ; Gutw. Flor. Glon. Okolic Lwowa," 1891, 

 p. 64, t. 3, f . 8 ; Roy & Biss. Scott. Desm. 1894, p. 40 ; Xorclst. Index 

 Desmid. 1896, p. 59 ; W. & G. S. West, Alg. S. England, 1897, p. 496 ; 

 Some Desm. IT. S. 1898, p. 319 ; Lutkem. Desm. Millstattersees, 1900, 

 p. 12 ; W. & G. S. West, Alg. N. Ireland, 1902, p. 57 ; Larsen, Ferskvand- 

 salger Vest-Gronl. 1907, p. 324. 



Cells minute, about as long as broad, deeply con- 

 stricted, sinus open, subrectangular, with a minute 

 acuminate extremity ; semicells elliptic-lunate with 

 the angles upwardly divergent, apex slightly concave, 

 each lateral angle widely emarginate-bifid. Vertical 

 view narrowly elliptic, with a minute spine at each 

 rounded pole. Cell-wall smooth. Chloroplasts axile, 

 one in each semicell, with a central pyrenoid. 



Zygospore unknown. 



Length (including the minutely spinate angles) 10- 

 14 ju,; breadth 11-15'5/x; breadth of isthmus 3-5*6 p, ; 

 thickness 5-6'5/x. 



ENGLAND. Burnham Beeches, Bucks ! Puttenham 



VOL. iv. 8 



