18 PROCEEDINGS OF THE ACADEMY OF 



HTAURASTRUM LeWISII. 



S. laeve, siuu amplissimo, spinulo parvo armato et cum angulo obtuso; 

 isthmo nulio : semicellulis a fronte late triangularibus, a vertice triangularibus 

 et cum angulis nonnihil tumidis, et rotundatis ; augulis spino maximo, ro- 

 busto, acuto armatis. 



Biam.— hong. cum. spin. 1-400'^ =-0025; lat. cum spin. 27-12000^^ = 

 •00225^^ Sine spin. : long. 1-600= -001666 ; lat. 13-12000 = -001666. Spin.: 

 long. 1-1500 = -000666. 



Smooth, with a very ample sinus, which is armed with a small spine and 

 hits a very obtuse angle ; isthmus absent ; semicells from the front broadly 

 triangular, from the vertex triangular, with the angles somewhat tumid and 

 rounded ; angles armed with a very large acute robust spine. 



Remarks. — This desmid is most closely allied to St. aristifermn, Ralfs., but 

 differs from it in outline as seen from the front, there being no maraellation 

 of the ends. The spines in the sinuses are also wanting in the European 

 species. 



COSMARICM SUBORBICULARE, Sp. nOV. 



C. parvum, suborbiculare, paulo longius quam latum, cum margine enormi- 

 ter crenato, vel crenato-undulato ; semicellulis a latere orbicularibus, a vertice 

 ellipticis ; sinu extra angustissimo scd intra nonnihil excavato ; cytiodermate 

 crasso, sparse verruculoso ; granulis in semicellulis singulis subdistantibus et in 

 seriebus elongatis, duobus (interdum unica) externis curvatis, et in seriebus 

 duobus interuis brevibus et rectis. 



Diam.— Lat. 14-12000^^ = -0012 ; lat. 16-12000 = -0013. 



Small, suborbicular, a very little longer than broad, with the margin irregu- 

 larly crenate, or crenate undulate ; semicells from the side orbicular, from 

 the vertex elliptical ; sinus very narrow, but within somewhat excavated ; 

 cytioderm thick, sparsely coarsely granulated ; granules subdistant, in each 

 cell arranged in one or two curved marginal series and in a central group of 

 two or three short rows. 



Remarks. — The arrangement of the granules in this desmid is peculiar, one 

 or sometimes two rows of large obtuse pearly granules placed at rather wide 

 intervals along the whole outer margins, and then in the centre of each semi- 

 cell a group of two or three, or even more short straight rows of three or four 

 similar but rather smaller granules. The isthmus is rather broad and short; 

 sometimes it has on it one or two granules. 



The doctor also exhibited drawings and specimens of the follow- 

 ing new species : 



^ Genus PLEUROT^IUM. 



V. BREVE. 



P. robustum, diaraetro 4 — 8 plo longius, in medio distincte constrictura 

 sed hand uudulatum, utroque polo nonnihil attenuatum ; apicihus truncatis 

 et nonnihil rotundatis; cytiodermate crassissimo, dense granulato-punctato ; 

 marginibus vel rectis, vel breve undulatis. 



/)(rt„j._-0008— -00095. 



Robust 4 — 8 times longer than broad, distinctly constricted but not undu- 

 hited in the middle, slightly attenuated towards the ends ; apex truncate and 

 somewhat rounded ; cytioderm very thick, densely minutely granulate ; mar- 

 gins either straight or shortly undulate. 



Remarks. — This species was sent to me by Dr. Billings, who obtained it 

 near Washington, D. C. The margins are sometimes straightish, but in others 

 there are three or more distinct short undulations, or rounded projections in 

 each half margin. The cell wall is excessively thick, especially at the end. 

 in many cases much thicker than the drawing. 



