ZOOLOGICAL AND BOTANICAL ASSOCIATION. 105 



points of affinity wanting with various neighbouring groups of Algae, 

 irrespective of the Diatomaceae. For instance, they approach the Pal- 

 mellaceous Algae by their gelatinous nature and likeness of form in some 

 species of Penium ; to the Ulvaceous Algae they approach through such 

 as Scenede8mii8 obtusus, connected with Merismopaedia; Spirotaenia con- 

 siderably resembles a joint of Spirogyra; while a form to be brought to 

 notice presently and its congeners point, I apprehend, to the Zygne- 

 maceae. 



The Desmidiaceae occur in shallowish, undisturbed ponds in open 

 exposed situations, such as little pools on boggy moors and commons, 

 permanent ponds in old quarries, &c. A few are met with in gently 

 flowing water. They are either mixed imperceptibly with the mud, or 

 disposed in a green stratum on the bottom, or projecting in little tufts, 

 or floating in little gelatinous masses on the surface, or forming a cloud- 

 like mass investing the submerged leaves of aquatic plants, or sparingly 

 scattered amongst the masses of filamentous Confervoids. Several species 

 are quite common, but as a group they are more local in their distribu- 

 tion, than, as a group, are the Diatomaceae, the commoner species of 

 which occur almost universally. 



Having thus tried, as briefly as I could, to communicate an epito- 

 mized account of the nature and appearance, and of the distinctive cha- 

 racters of this group of Confervoid Algae, and because an explanation 

 seems to be due for obtruding so much that is not new, I would beg 

 again to remark that I have undertaken it for the use only of those of 

 our members who may be unacquainted with the facts and details brought 

 forward. I will now pass on to describe my new forms, being that por- 

 tion of this communication to which any interest will be likely to attach 

 on the part of those who are experienced. 



I have now to bring to notice an Alga which, to the naked eye in 

 the mass, and perhaps at first sight under the microscope, does not at 

 once strike the observer as belonging to the Desmidiaceae. The organism 

 in question forms rather dense masses of filaments, sometimes an inch or 

 two or more in length, attached to aquatic plants, and, in the mass, is of 

 a bright and beautiful green, and of an elegant appearance, like " floss 

 silk" in the water. When placed under the microscope, the filaments 

 are seen to be composed of very greatly elongated joints, of moderate 

 diameter, with truncate ends, and possibly might, at a hasty glance, be 

 taken for a Mesocarpus, or some allied form. Probably the first circum- 



ZOOL. & BOT. SOC. PROC. VOL. I. P 



