ARCHER, OX DESMIDIACEJE. 235 



Now Fig. 7 of the present Plate seems to indicate that the 

 vegetative energ}' is not necessarily arrested ; for between the 

 central growth (of the first case in A. Incus figured), and each 

 of the original segments, a new expansion has been formed — 

 the whole, that is, the older segments and the now three in- 

 tervening portions (the middle one being the older) forming 

 still one uninterrupted cavity, and filled with endochrome 

 throughout. The entire structure, under a low power, might 

 be mistaken for a Scenodesmus; but, when sufficiently 

 magnified, its real nature is quite apparent. The specimen 

 (Fig. 7) occurred amongst several others in the condition 

 figured with my former paper (Fig. 11), both mixed with 

 multitudes in the normal state, some in the dividing con- 

 dition. There does not seem any readily assignable limit to 

 the extent to which this monstrosity might be carried ; yet, 

 even supposing it had attained some considerable length, and 

 that the extraordinary structure should survive its own 

 fragility, a time must come, I conceive, as in normal indivi- 

 duals, when the vegetative impetus would be spent, and when, 

 therefore, further increase by mere self-division (in this case, 

 however, abnormally and abortively undertaken) would subside. 



Fig. 6 represents a remarkable mycelioid growth occurring 

 within a Closterium lunula, noticed in the paper alluded to, 

 read to the Society (page 472, /. c), remarkable on account of 

 the impossibility, except on Pringsheim's theory in regard to 

 Pythium {vide preceding Paper), of accounting for the origin 

 of such a curious internal parasite. 



Description of a New Species of Cosmarium, and of a Neiv 

 Species of Xanthidium. 



Family.— DESMLDIACE.E. 



Genus. — Cosmarium (Corda). 



Cosmarium Portianum (sp. nov.). 



Specific characters: Frond deeply constricted; segments, 

 in front view, broadly elliptic, rough with minute, scattered, 

 pearly granules, constriction deep, wide, isthmus forming a 

 short neck ; end-view elliptic. 



Locality: Pools, Dublin and Wicklow Mountains; not 

 uncommon. 



General description : Frond minute, compressed, in front 



