COSMARIUM. 361 



Hab. Aslulown Forest, and near Cross in Hand : Mr. 

 Jenner. Penzance : Mr. Ralfs. 



Tills species differs from X. fascicuJatum 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 

 ivitk sporidia, copulating, at length hearing two spores 

 transversely divided into halves. 

 Derivation. From Kv\iv8po9, a cylinder, and Kvcrris, a cell. 



1. Cylindeocystis 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. II. II. 

 Aberdeen: Dr. Dickie. Galway : BPColla. 



This is a particularly interesting production, as It seems to 

 form a direct link bet\\"een the ProtococcoidecB and the Des- 

 midece, and by ISIeneghini himself is placed in the family 

 NostochinecB. 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. COSMAEIUJNI Corda. 



Char. Frond constricted in the middle. Segments frc- 

 quently as broad and sometimes broader than long, neither 



