DUBLIN MICROSCOPICAL CLUB. 201 



the Club in Mr. Archer's drawing would seem much to resemble 

 a new species lately described by Wittrock — Staurastrum hiden- 

 tatum (y^\itv.,m. 'Auteckningar om Skandiuaviens Desmidiaceer,' 

 for a copy of which highly interesting memoir Mr. Archer had 

 very much to thank the author, whose figure he referred to), but 

 that is a considerably smaller form, the spines at the angles re- 

 duced to two short, rounded, blunt processes ; but above all the 

 endochrome is depicted as forming vertical chlorophyll- plates 

 radiating from the centre, thus distinctly separating the two 

 forms ; for it is quite clear that whatever may be its bearing in a 

 generic point of view, the character in question abundantly dis- 

 tinguishes species, though one can, as yet, hardly think that the 

 natural diversity thus evinced has more than a specific signifi- 

 cance as regards certain forms naturally congeneric with certain 

 others, so far as relates to their outward configuration, but these 

 latter presenting a different internal arrangement of contents. 

 The species really most nearly allied to the present is St. tumidum 

 (Breb.), as they resemble each other a good deal in general outline 

 and in possessing a very thickened conspicuous mucous envelope, 

 but the present is a somewhat smaller form, the lateral margins in 

 the end view concave at the middle (instead of convex), and, as 

 has been mentioned, provided Avith two elongate, closely posed 

 spines at each angle, one only of which is conspicuous in the end 

 view (not with a single nipple-like tubercle). They agree in the 

 punctate character of the cell-wall, best seen when evacuated of 

 contents, though readily enough perceptible in the ordinary con- 

 dition, especially at the vacant intervals between the chlorophyll- 

 bands. 



Mr. Archer presented a drawing of another fine form referable 

 to Staurastrum — if, indeed, the genus Didymocladon were to be 

 considered admissible it would fall under it. This is a very 

 elegant I'orm, its beauty, however, somewhat interfered with by 

 the thick and very striated mucous envelope by which it is sur- 

 rounded, not attempted to be delineated in the drawing. It is 

 large, constriction forming a wide, acute-angled sinus, the pro- 

 cesses long, slender, divergent, lower ones horizontal, upper 

 directed upward (each tier being on the same plane, all lateral, 

 none dorsal), and with three or four shallow marginal denticula- 

 tions, apices 3- or 4-fid, in end view 5-radiate, angles produced. 

 It will thus be seen this beautiful form to a certain extent re- 

 sembles St. {Didymocladon) furcigerum (Breb.), but it is con- 

 siderably larger, the rays longer and shallow-denticulate (not 

 minutely granulate), radiate in end view (not tri- or quadrangu- 

 lar). It might, of course, also call to mind, to some extent, ^S*^. 

 pseudofurcigerum (Eeinsch, in 'Algenflora des mittleren Theiles von 

 Pranken,' p. 169, t. xi, fig. 2), but in that species the processes 

 are short, stout, minutely denticulate, apices binate, end view 3- 

 angular. The latter form differs, too, from the present, in pos- 

 sessing a pair of processes above, and radiating to each side of 

 that projected horizontally from each opposite lateral extremity. 



VOL. XII. NEW SER. P 



