DUBLIN NATURAL HISTOEY SOCIETY, 75 



taming scattered rounded large granules, and frequently retracted from 

 the margin of the frond, so as to leave a hyaline border. Micrasterlas 

 rotata and M. denticulata differ in the following particulars : — The for- 

 mer is notably a larger species than the latter ; in front view, in the 

 former, the basal lobes are twice, the middle lobes thrice dichotomous — 

 in the latter both basal and middle lobes are bat twice dichotomous, 

 thus making in the former the ultimate subdivisions of the middle lobes 

 eight (and this additional dichotomy makes itself apparent at an early 

 stage in the growth of the young segments), and making in the latter 

 the ultimate subdivisions of the middle lobes but four only (in the for- 

 mer, therefore, the middle lobes are wider in proportion than in the 

 latter) ; in the former the ultimate subdivisions of the basal and middle 

 lobes are acutely bidentate — in the latter they are truncato-emarginate, 

 with more or less rounded, sometimes subacute, angles ; in the former 

 the end lobe is greatly more distinguishable in character and appearance 

 from the others than in the latter ; in the former, the outline of the end 

 lobe is narrowed below, inflated above the base, again contracted, and 

 again dilated and spreading at the extremity, — in other words, more or 

 less of a narrow campanulate outline (the adjoining upper margin of 

 the middle lobes closely approximating thereto by a corresponding out- 

 line) — in the latter, the end lobe is simply cuneate, with the sides 

 somewhat concave ; in the former, the end lobe is distinctly exserted 

 beyond the general periphery of the frond — in the latter, it is not ex- 

 serted, its outer margin being continuous with that of the frond ; in the 

 former, the angles of the end lobe are produced, divergent and bidentate, 

 in the latter, its external angles are bluntly rounded ; in the former, 

 the central emargination of the end lobe is not so deep as in the latter ; 

 in the former, the endochrome is more dense within the end lobe, es- 

 pecially at both of its margins, than elsewhere in the frond, giving it a 

 turgid apj)earance, and rendering the campanulate outline more strik- 

 ing, — in the latter it is not so. In the side view in the former (Fig. 

 9), the frond is stouter and more turgid than the latter (Fig. 6), its 

 sides less concave. In the end view, the former is stouter, and the 

 outline is broadly fusiform, with a solitary central slightly elevated 

 rounded projection at each side (Fig. 10) — in the latter the outline is 

 more slender, and is lanceolate, with 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. denti- 

 culata. 



I am thus particular in contrasting these two species with one ano- 

 ther, because, while I believe them to be quite as distinct as any two 

 allied species need or can be, and while (though having seen multitudes 

 of specimens of both) I have never seen one in which there seemed any 

 difficulty in deciding to which species it belonged, I imagine, never- 

 theless, as before intimated, that there appears to be some misconception 

 prevalent as to the distinctness, or as to the actual characters of these 

 two species. In the " Quarterly Journal of Mic. Science, N. S.," Vol. i., 



