72 DUBLIN NATURAL HISTOKT SOCIETY. 



to : far from it. I am convinced that, in many departments of Natural 

 History, very many of the species descrihed 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 — ALG^. Order — Chloeosperme^. 

 Family — Desmidia ce^. 

 Genus — Micrasterias i^Ag. et aliorum, non JEhr.) 



Micrasterias Thomasiana (mihi, sp. nov.) 



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 eleva- 

 tions, their apices directed outwards ; the lateral lobes dichotomously 

 divided, their ultimate subdivisions bi- or tri-dentate, or sometimes qua- 

 dridentate, not tapering ; end lobe whoUy included, acutely emarginate, 

 its angles acute. End view — the body of the segment lanceolate, the 

 projections very conspicuous, together presenting a doubly hastate out- 

 line. 



_ Locality:— A large pool near the " Old Gable," Featherbed Moun- 

 tain, and sparingly elsewhere in the vicinity. 



Measurements":— Length of frond, -^^j; breadth of frond, j-^; 

 greatest depth of frond, ^J-^, inclusive of the projections ; exclusive of 

 the projections, ^^q- of an inch. 



General Description : — Frond orbicular, smooth ; segments in front 

 view five-lobed, having the lateral lobes dichotomously incised, furnished 

 at the base with three conspicuous hollow projections or protuberances, 

 the middle one conical, rounded ; the outer distant from each other rather 

 less than one-third the diameter of the frond, tapering, curved, some- 

 what elongate, emarginate at the extremities, sometimes with a tooth 

 on the upper margin, laterally divergent from each other, but approxi- 

 mate to those of the opposite segment ; basal lobes with two little apicu- 

 late conical elevations on the surface, apparent only on the empty frond, 

 their apices directed outwards, equidistantly placed at the base of each 

 of the primary subdivisions of the lobes, and on a level with the extre- 

 mity of the primary incision ; middle lobes with three similar elevations, 

 two placed at the base of each of the primaay subdivisions, on a level 

 with the extremity 0/ the primary incision, and the other placed at the 

 base of the lobe, distant about as far beneath the other two as they are 

 from each other, the two elevations of each of the basal, and the two 

 outer of each of the middle lobes forming regular series semicircularly 

 disposed ; end lobe with two similar elevations, one placed beneath the 

 other, the outer somewhat within the semicircular series of elevations of 



