2-14 ARCHER^ ON A NEW SPECIES OF MICRASTERIAS. 



three slight^ less rounded and less elevated projections at the 

 middle at each side (fig. 7). In my mind, M. rotata is a 

 handsomer and more striking species than M. denticulata. 



I am thus particuhu* in contrasting these two species with one 

 another, because, aa hile I believe them to be quite as distinct 

 as any tno allied species need or can be, and while (though 

 having seen multitudes of specimens of both) I have never seen 

 one in Avhich there seemed any difficulty in deciding to which 

 species it belonged, I imagine, nevertheless, as before inti-. 

 mated, that there appears to be some misconception prevalent 

 as to their distinctness or as to their actual characters. ]\Ir. 

 Lobb,^ in his interesting paper, describing the growth of the 

 nascent segment in dividing fronds of Micrasterias, through- 

 out calls liis specimens M. denticulata, but he fyiires M. 

 rotata. Again, Dr. Wallich,t in the first two — and only two 

 as yet published — of a series of papers descriptive of Desrai- 

 diacete discovered in Bengal, affirms his belief that M. rotata 

 and M. denticulata, met with by him very sparingly in that 

 country, are really but vai'ieties of one species. But he 

 adopts the same course, indeed, with many other allied 

 species. I am compelled, hoAvever, very deferentially to 

 differ from him. Mr. Ealfs himself, J indeed, expresses 

 '^ some doubt whether this plant [M. rotata] is not a variety 

 of M. denticulata, as the angles are sometimes merely acute, 

 instead of being prolonged into teeth ; but I surely think 

 the claims of each to specific rank do not depend upon this 

 one or upon any one character, but, as I have indicated 

 aboA'e, are founded on many and constant points of dift'erence. 

 It is certainly not an argument for their specific identity that 

 they possess several characters in common, and, so far as I 

 see, I have above indicated all such, leaving out of question 

 those that are strictly generic. Surely the ultimate, constant, 

 and obvious characters, possessed by one and not by the 

 other, are those upon which we must rely, and I conceive 

 those I have above pointed out are abundantly sufficient to 

 separate those tAvo species. It is to be at once conceded, 

 indeed, that sometimes with them, as Avith other species, slight 

 variations occur, such as a greater interval iDctAveen the lobes, 

 more or less acuteness of the teeth^ or such like accidental 

 circumstances, but I aver that there is ahvays a tout ensemble 

 rendering the identification a matter of no difficulty, I am 

 glad to say I am sustained in this view by that of so distin- 



* 'Quarterly Journal of Microscopical Science,' N. S., vol. i, p. 1, 

 January, 1861. 



f 'Annals of Natural History,' 3rd ser., vol. v, p. 2S0. 

 I 'British Pesmidise/ p. 71. 



