104 BRITISH DESMIDIACE^E. 



spiny zygospores, it was necessary that it should be re- 

 named. 



A. controversies is probably the smallest species of the 

 genus. It resembles A. crassus in outward form, but is much 

 smaller and more delicate, and the vertical view is elliptic 

 with broadly rounded poles. 



6. Arthrodesmus phimus Turn. 

 (PL CXV, figs. 15, 1(5.) 



Arthrodesmus phimus Turn. Fresh w. Alg. E. India, 1893, p. 136, t. 12, f. 9 ; 

 Nordst. Index Desmid. 1896, p. 200; W. & G. S. West, Freshw. Alg. 

 Ceylon, 1902, p. 192, t. 22, f. 21. 



Cells small, about as long as broad (without the 

 spines), sometimes longer, sometimes broader, deeply 

 constricted, sinus subrectangular with a rounded 

 or an acuminate extremity ; semicells obver^eiy 

 subtriangular or widely cuneate, sides convex, apex 

 widely retuse, each angle slightly rounded and fur- 

 nished with a very short divergent spine. Vertical 

 view narrowly elliptic, poles rounded, each with a very 

 short spine. Cell-wall smooth. 



Zygospore unknown. 



Length 1 9*5-26 ^ ; breadth without spines 20-25*5 ^ ; 

 length of spines 3-4 //, ; breadth of isthmus 6'5-7'5/x. 



Geogr. Distribution.- -India. Ceylon. 



The typical form of this species is not known to occur in 

 the British Islands. 



Var. occidentalis W. & G. S. West. (PL CXV, 



fig. 17.) 



A. phimus var. occidentalis W. & G. S. West, Alg. N. Ireland, 1902, p. 59, 

 t. 2, f. 17. 



A small variety, with the cells broader than lono- 



*> ^ O ? 



the angles less produced, and the sinus somewhat less 

 open. 



Length 14-14'6/x,; breadth without spines 16'3- 

 17*3 (ji, with spines 19-19*4 /x ; breadth of isthmus 5*7- 

 6*2 p, ; thickness 7*2 p.. 



ICELAND. Louo'h Anna. Donegal ! 



O ' O 



