243 AKCHERj ON A NEW SPECIES OF MICRASTERIAS. 



is obtained^ that all these projections^ which render this form 

 so remarkable, stand out in all their striking prominence, 

 giving the general outline which suggested to me the term 

 doubly hastate. (Figs. 4 and 5.) In end view, too, arc 

 seen the summits of the superficial projections directed out- 

 wards, imparting to the boundary of each lobe, the outer edge 

 of which is now towards the observer, a somewhat inversely 

 subcampanulate outline. In a somewhat oblique, partially 

 front, partially lateral view, the several projections stand out 

 in a crowded, mixed, very puzzling manner. In by far the 

 greater number of examples the basal and middle lobes are 

 thrice dichotomous, the ultimate incisions being, however, 

 shallow, but mostly quite distinct ; the ultimate subdivisions 

 are, therefore, eight to each lobe, and rather acutely bidentate. 

 But it occasionally happens that the tertiary incisions are 

 obsolete, or not appreciably deeper than the intervals between 

 the teeth, when the lobes cannot be said to be more than 

 twice dichotomous, causing the ultimate subdivisions to be 

 but four in number, and then mostly tridentate or quadriden- 

 tate. The end lobe is narrow, acutely emarginate at the 

 middle, its lateral angles acute, and wholly included — indeed, 

 slightly beneath the general periphery of the frond. 



It is with great pleasure I avail myself of the privilege 

 kindly accorded to me to name this species after Mrs. Her- 

 bert Thomas, whose paper on " Cosmarium,^^"^ has, doubtless, 

 been pervised with much interest by every student of the 

 Desmids, and I am happy at having the opportunity of thus 

 evincing my own humble appreciation of her researches. I 

 consider that all praise is due to those ladies who honour our 

 studies by a personal co-operation ; and I feel, indeed, that I 

 am far more complimented than complimenting in being per- 

 mitted to dedicate this species to Mrs. Thomas. 



Affinities and dijferences. — I believe there are only two 

 species with which there is any chance of this Micrasterias 

 being confounded, and they are 31. rotata, Ralfs, and M. 

 denticidata, Breb., but with the latter I conceive it has the 

 greater affinity. But as I imagine there is some misappre- 

 hension prevalent in regard to the diflFerences and distinctions 

 of the two species just mentioned, it may not be out of place, 

 if, before contrasting them with this new species, I should 

 draw attention to their own mutual points of similarity and 

 of difference. M. rotata, Ralfs, and M. denticidata, Breb., 

 agree in having an orbicular frond of large size, smooth, 

 without spines, papillse, or granules, their segments five- 



* 'Quarterly Journal of Microscopical Science,' Trans., vol. ill, pp. 33, 

 36. 



