ARCHER, ON A NEW SPECIES OF MICRASTERIAS. 239 



who over-multiply species in the other. And those who may- 

 be disposed to question the actual distinctness of certain of 

 these Desmidian species, and who may draw their arguments 

 from a hasty or a single examination, or from figures, or 

 from preconceived ideas, I would just beg to suspend their 

 judgment until they make a careful comparison of the living 

 specimens side by side, drawn from different sources and on 

 different occasions ; for, with the greatest deference, I main- 

 tain that it is Nature that should speak, and by Nature that 

 we should be guided, and not by opinion or theory, nor by 

 any preconceived scheme, however ingeniously devised, by 

 which, after all, probably good species are imwittingly 

 grouped together into Avhat are nothing but small subgenera 

 (though, without adopting that name, called indeed species), 

 the so-called vai'ieties. Nature compelling the distinctions at 

 last to be acknowledged, being the true species. I do not, 

 however, mean to convey that I at all imagine species to be 

 invariable, and that authors, in disallowing certain so-called 

 species, in so doing always fall into the error I have alluded 

 to ; far from it. I am convinced that, in many departments 

 of natural history, very many of the species described in 

 books exist there only, and are not supplied by Nature ; and 

 I only mean to say that it appears to me the opposite mistake 

 is more frequently fallen into now-a-days than is generally 

 thought ; and my remarks are more especially with reference 

 to the Desmidiacese. 



Class — ALGiE. Order — Chlorosperme^. 



Family — Desmidiace^. 



Genus — Micrasterias {Ag. et aliorum, non Ehr.) . 



Micrasterias Thomasiana, sp. nov. mihi. 

 Specific characters. — Frond orbicular, smooth ; segments 

 five-lobed, furnished at the base with three stout, conspicuous, 

 prominent, hollow projections, the middle conical, rounded, 

 the outer tapering, curved, elongate, emarginate, divergent; 

 lobes closely approximate throughout, each bearing two or 

 three superficial, regularly disposed, apiculate elevations, 

 their apices directed outwards ; the lateral lobes diehoto- 

 mously divided, their ultimate subdivisions bi- or tri-dentate, 

 or sometimes quadridentate, not tapering; end lobeVholly 

 included, acutely emarginate, its angles acute. End-view — 

 the body of the segment lanceolate, the projections very con- 

 spicuous, together presenting a doubly hastate outline. 



