150 CONJUGATED. 



oval, lying in cells which are considerably inflated for 

 their accommodation. 



Zygnema Grevilleanum, Annals and Mag. of Nat. Hist, 

 vol. x. p. 38. 



Hob. Cheshunt and its vicinity : A. H. H. Framfield : 

 Mr. Jenner. Dolgelley : Mr. Ralfs. Turf Dyke, near 

 Ardrossan : Major Martin. 



" To this~ fine species I have assigned the name of Dr. 

 Greville, author of the excellent ' Algae Britannicae,' as a 

 slight mark of personal respect, as well as an acknowledge- 

 ment of the eminent services rendered by that gentleman 

 to natural history." 



22. ZYGNEMA IN^QUALE Hass. 

 Plate XXXIT. Figs. 1, 2. 



Char. Filaments of smaller diameter than those of Z. Gre- 

 villeanum. Cells about Jive times as long as broad, and 

 enlarged on the side from which the tubes of communica- 

 tion arise. Sporangia oval. 



Hob. Cheshunt: A. H. H. 



This is not a common species. I have no doubt but that it 

 is distinct. 



23. ZYGNEMA SUBVENTRICOSUM Hass. 

 Plate XXXII. Figs. 3, 4, and 5. 



Char. Diameter of the filaments about equal to these of 

 Z. commune. Cells usually Jive or six times as long as 

 broad. Sporangia oval, occasioning the cells in which they 

 are placed to assume a ventricose form. 



Zygnema ventricosum Hassall, in Annals of Nat. Hist, 

 vol. x. pp. 38, 39. 



Hob. Cheshunt and its vicinity : A. H. H. Heathfield ; 

 in a pond near Boar's Head, Ramslye Rocks; and 



