Mr. J. Ralfs on the British Desmidiese. 401 



69. A. Gyllenhaliy Kirb. ? , Gyll., Genu., Steph., Schonh, 



— unicolor, Kirb. ^ , Germ., Steph., Schonh. 



— jtEthiops, Gyll. vol. iii. 



This insect appears to be extremely rare in the south, and very 

 local in the north of England. I once found it abundantly, in 

 company with Ap. Spencii, in a valley just beyond the White Nab, 

 on the sea-coast south of Scarborough in Yorkshire, upon Vicia 

 Cracca, the beginning of August 1837, which gave me an op- 

 portunity of identifying the sexes of both species beyond all 

 doubt, and the pleasure of supplying many cabinets with speci- 

 mens, since v^^hich I have never met with it, nor have I heard of 

 its capture in the south of England. 



70. A. Melilotiy Kirb., Germ., Steph., Schonh. 



— bifoveolatum, Steph. 



Few cabinets contained this species until I had the pleasure of 

 supplying them. I met with it near Knaresborough in Yorkshire 

 in profusion upon the melilot trefoil {Trifolium officinale) in Sep- 

 tember ; it occurs very sparingly in the south j I have occasionally 

 found a few specimens in Charlton sand-pits upon the same plant, 

 and it is the only locality that I am acquainted with in the vici- 

 nity of London. Mr. S. Stevens has taken it at Bury-hill near 

 Arundel in August, and also at Charlton in June. 



I have a foreign specimen of Ap. aciculare from Germar, who 

 informs me that it is found in Germany upon Cistus Reliant he- 

 mum, but very rarely ; it has been recorded as British, yet I have 

 never seen an indigenous example. 



LVII. — On the British Desmidiese. By John Ralfs, Esq., 

 M.R.C.S., Penzance*. 



[With a Plate.] 



ScENEDESMUS, Meyen (Arthrodesmus, Ehr,). 



Fronds composed of few (two to ten), cylindrical, fusiform or ob- 

 long cells, arranged in one or two rows. 



The cells are always entire and mostly fusiform or oblong, al- 

 though in some species the outer ones are lunulate. They arc 

 few in number, varying from two to ten, and are placed side by 

 side in one or two rows and united by a hyaline mucus. 



In this genus the specific characters depend on the number, 

 position and form of the cells. It however seems probable that 



• Read before the Botanical Society of Edinburgh, June 13, 1844. 



