ARCHEK, ON A NEW SPECIES OF COSMARIUM. 247 



regarded in what I humbly conceive to be their true light ; 

 and if Micrasterias Thomasiana, with these remarks of mine, 

 should afford any student of the Desmidiacese the smallest 

 interest, and in so doing should at all contribute to the end 

 alluded to_, my purpose will have been attained. 



Description of a New Species of Cosmarium (Corda), of 

 Staurastrum (Meyen), of Two New Species of Closte- 

 RiuM (Nitzch)j and of Spirot/Enia (Breb.). By Wm, 

 Archer. 



Family — DESMiDiACEiE. 



Genus — Cosmarium^ Corcla. 

 Cosmarium tuberculatum, sp. nov. 



Sjyecific characters. — Frond very minute, constriction very 

 obtuse and shallow; segments in front view broadly ellipticj 

 outer margin bordered by a few very minute^ opaque tubercles 

 or granules ; end view broadly elliptic. 



Locality. — A small pool, near the ice-houses, on the Pipers- 

 town road, county of Dublin. 



General description. — Frond very minute ; in front view 

 about one fourth longer than broad ; constriction wide, shal- 

 low, forming an obtuse angle ; isthmus wide ; segments 

 broadly elliptic, outer margin bordered by a few (5 — 7, often 6) 

 very minute opaque superficial tubercles or granules; side 

 \iew narrower, about twice as long as broad; constriction a 

 mere gentle depression or concavity at each side, segments 

 forming about two thirds of a circle, outer margin, as before, 

 bordered by a few minute, opaque tubercles ; end view broadly 

 elliptic. Sporangium unknown. 



Measurements. — Length of frond, -n-^nro ^o tttit^ breadth, 

 WaTr to rv i,\. l i' ; depth, .. -'-, „ of an inch. 



Plate XII, fig. 11, front view; fig. 12, side view; fig. 13, 

 end view; figs. 14 and 15, dividing fronds. All magnified 

 400 diameters. 



Affinities and differences. — The very minute size, combined 

 with the obtuse, shallow, but decided constriction, and, above 

 all, the outer margin of each segment being bordered by the 

 minute, opaque, or dark granules, render this little species 

 very distinct, causing it to be almost unnecessary to compare 



