74 DUBLIN NATURAL niSTOEY SOCIETY. 



made out; they are quite conspicuous on the empty frond. (Fig. 2.) 

 That these curved projections are hollow is indicated by my having seen, 

 in an empty segment, an infusorium making its way up into and down 

 again from one. On the empty frond, also, the superficial apiculate pro- 

 jections are readily seen ; occasionally one appears emarginate or divided, 

 showing a double apiculus. It is not, however, until an end or trans- 

 verse view 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. (Pigs. 

 4 and 5.) In end view, too, are seen the summits of the superficial projec- 

 tions directed outwards, imparting to the boundary of each lobe, the outer 

 edge of which is now towards the observer, a somewhat inversely-sub- 

 campanulate 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, very shallow, but mostly quite distinct ; the ultimate subdi- 

 visions 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 triden- 

 tate or quadridentate. 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 ac- 

 corded to me to name this species after Mrs. Herbert Thomas, whose 

 paper on Cosmarium, published in the "Quarterly Journal of Micro- 

 scopic Science, Trans." vol. iii., pp. 33-36, has doubtless been perused 

 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 permitted to 

 dedicate this species to Mrs. Thomas. 



Affinities and Differences : — I believe there are only two species 

 with which there is any chance of thisMicrasterias being confounded, and 

 they are M. rotata (Ealfs) and 31. denticulata (Breb.), but with the lat- 

 ter I conceive it has the greater affinity. But as I imagine there is some 

 misapprehension prevalent in regard to the differences 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. Micrasterias rotata 

 (Ralfs) and M. denticulata (Breb.) agree in having an orbicular frond of 

 large size, smooth, without spines, papillae, or granules, their segments 

 five-lobed, the basal and middle lobes dichotomously divided ; the lobes 

 closely approximate throughout, widening the entire way from the base, 

 the ultimate subdivisions not being attenuate, and the endochrome con- 



