78 DITBLTN NATURAL HISTORY SOCIETY. 



other species of Micrasterias with which I am acquainted that possess 

 any processes or projections directed in a different plane from that of the 

 frond, are M. muricata (Ralfs) and M. Americana (Ralfs). In those 

 species, however, the projections are at the external margin of the seg- 

 ment, not at their base ; and the entire form, and structure, and appear- 

 ance of the frond is wholly and completely different, any characters in 

 common being, of course, those only of generic value. 



Some may think, I fear, that I have gone to unnecessary length in 

 carrying out the intention of this paper. I can only apologise by say- 

 ing I am anxious that these common species of Micrasterias, M. rotata 

 and M. denticulata, remarkably beautiful and favourite microscopic ob- 

 jects, should be regarded in what I humbly conceive to be their true 

 light; andif 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. 



FRIDAY, JUNE 7, 1861. 

 "William Andrews, M. R. I. A., President, in the Chair. 

 The previous Minutes were read and signed. 

 Mr. William Archer read the following paper : — 



DESCRIPTION OF A NEW SPECIES OF COSMARIUM (cORDA), OF STAIJRASTRUM 

 (mEYEn), of TWO NEW SPECIES OF CLOSTERIITM (nITZSCh), AND OF 

 SPIROTiENIA (BREB.). 



Family— DESMIDIACE^. 



Genus — CosMARniM {Gorda.) 



Cosmarium tuberculatum (sp. nov.) 



Specific Characters : — Frond very minute, constriction very obtuse 

 and shallow ; segments in front view broadly elliptic, outer margin bor- 

 dered by a few very minute opaque tubercles or granules; end view 

 broadly elliptic. 



Locality : — A small pool, near the ice-houses, on the Piperstown 

 road, county of Dublin. 



General Description : — Frond very minute ; in front view about ^th 

 longer than broad ; constriction wide, shallow, 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 

 view narrower, about twice as long as broad ; constriction a mere gentle 

 depression or concavity at each side, segments forming about |rds of a 

 circle, outer margin, as before, bordered by a few minute opaque tu- 

 bercles ; end view broadly elliptic. Sporangium unknown. 



