COSMARIUM. 361 



Hob. Ashdown Forest, and near Cross in Hand : Mr. 

 Jenner. Penzance : Mr. Ralfs. 



This species differs from X. fasciculatum principally in the 

 spines being single and not in pairs as in that species. 



" In the centre of each segment, on both surfaces, is a pro- 

 jection similar to that described under X. furcatum, but less 

 evidently dentated." Ralfs. 



57. CYLINDROCYSTIS Menegh. 



Char. Frond mucous, indefinite. Corpuscles cylindrical, filled 

 with sporidia, copulating, at length bearing two spores 

 transversely divided into halves. 



Derivation. From Kv\wpos, a cylinder, and KVO-TLS, a cell. 



1. CYLINDROCYSTIS BREBISSONI Menegh. 

 Plate XCII. Fig. 17. 



Char. Cells cylindrical, two or three times longer than broad, 

 with rounded extremities. 



C. Brebissoni Menegh., Monog. Nostoc. Italic. 



Hab. Sussex : Mr. Jenner. High Beech : A. H. H. 

 Aberdeen: Dr. Dickie. Gal way : M ( Colla. 



This is a particularly interesting production, as it seems to 

 form a direct link between the Protococcoidece and the Des- 

 midecR, and by Meneghini himself is placed in the family 

 Nostochinece. The conjunction of the cells, as well as their 

 great size and regular form, have induced me to refer it to the 

 Desmidece, in which the phenomenon of union of the cells is 

 of such frequent occurrence. The frond does not appear to 

 be divided in the centre as in most true Desmidece. 



58. COSMAEIUM Corda. 



Char. Frond constricted in the middle. Segments fre- 

 quently as broad and sometimes broader than long, neither 



