ARTHRODESMUS. 97 



A small variety with the spines very long and 

 upwardly divergent to the same extent as in var. 

 validus. 



Length without spines 14 p.; breadth without spines 

 11'5/x; length of spines 2 1-25 /x; breadth of isthmus 

 57 /x. 



SCOTLAND. --Small loch near Cearnabhall, Lewis, 

 Outer Hebrides (in the plankton) ! 



Geogr. Distribution. Poland. United States. 



This variety is well characterized by the great length of 

 the spines as compared with the size of the cell-body. 



Var. subquadratus WV & G. S. West, (PI. CXIV, 



? A. Incus forma quadrat a Schmidle, Beitr. alp. Alg. 1896, p. 26 (sep.), 



t. 16, f. 10. 

 A. In cus var. subquadratus W. & Gr. S. West, Alg. S. England, 1897, p. 



496, t. 7, f . 20. 



A small variety with the cells much less constricted 



/ 



than usual; semicells subquadrate or rectangular- 

 quadrate, sides and apex very slightly convex. 



Length without spines 15-17ju,; breadth without 

 spines 11 /x ; length of spines 5*5-7 JJL; breadth of 

 isthmus 7'5/x; thickness S p.. 



ENGLAND. Chobham Common, Surrey ! 



It is possible that "forma qnadrata ." described by Schmidle 

 from the Tyrol is identical with this variety, but Schmidle's 

 figure is poor. His description reads " aculeis divergentibus, 

 apicibns tnmcato-rotimdatis, lateribns fere parallelis vix vel 

 non concavis." 



2. Arthrodesmus triangularis Lagerh. 

 (PL CXIV, figs. 11-13, 17.) 



Arthrodesmus triangularis Lagerh. Bidr. Amerik. Desm.-fl. 1885, p. 244, 

 t. 21, f . 22 ; De Toni, Syll. Alg. 1889, p. 1061 ; Eacib. Desm. Tapakoomas. 

 1895, p. 33 ; W. & Gr. S. West, Alg. N. Ireland, 1902, p. 58 ; Scott. 

 Fresh w. Plankton, 1. 1903, p. 528; Freshw. Alg. Orkneys and Shetlands, 

 1905, p. 24; Further Coiitrib. Freshw. Plankton Scott. Lochs, 1905, 

 p. 485; Freshw. Alg. Burma, 1907, p. 211, t. 15, f. 7; Brit. Freshw. 

 Phytoplankton, etc., 1909, p. 181 ; Phytoplankton Engl. Lake Distr. 

 1909, p. 138. 



? A. Incus forma rotundata Racib. Desm. Nowe, 1889, p. 96, t. 6, f. 16. 



A. Incus var. triangularis Lagerh. in Nuova Notarisia, IV, 1893 p. 182. 



VOL. IV. 7 



