142 FRESH-WATER ALGJ5 OF THE UNITED STATES. 



Segments tliree-lolied, basal lobes long, subeonical, acute ; termina. lobes slcndor, forked at the 

 end, with the divisions much shorter than the basal lubes. (Bailey.) 



jTI. qiiadrala, Bailey. 



M. areuatae siniilis, sed duplo major, -semieellularum lobi basales minus arcuati, basi inQati, 

 apice bidcntati et cjtioderma irregulariter granulatum. (R.) 



Z»ia?n.— 0.0043"— 0.0049". 



Syn. — M. quadrala, Bailey, Microscopical Observations : Smithsonian Contributions, vol. ii. 

 Large quadrangular, three-lobed, basal lubes elongated, slightly curved, bideutate ; terminal 

 lobes with two slender transverse bidentate projections. Bailey. 



III. flispiitata, Wood. 



M. magna, fere tarn longaquam lata, subpinnatisecta, sinu acuto, lobisaeqnalibus ; scmicellulispro- 

 funde trilobis, lobis basalibus in apieem acute bidentatum valde attenuatis; lobo pulari valde 

 dilatato, dorso rotundato, angulis lateralibus acutissimis. 

 Long. ^15/=. 005". Lat. 7|g^" = .004". 



Syn. — 3Iicrasterias iiicisa, Ktz. Bailey, Microscopical Observations: Smithsonian Contribu- 

 tions, 1860. 

 Haud llicrasteria iucisa, Kutzing, Spec. Algarum, p. 171. 

 Tetrachastrum Amer-icaiium, Akcu.'E.b., Pritchard's Infusoria, 1800, p. 725. 

 Hah. — South Carolina; Georgia; Florida; Rhode Island ; Bailey. Penn.sylvania ; Wood. ' 



M. large, about as long as broad, subpinnatisected ; sinuses acute; semicells profoundly trilo- 

 bate ; basal lobes strongly attenuate into the acutely bidentate apex ; distal lobes strongly 

 dilated, rounded, with their lateral angles bidentate ; end lobe broadly dilated, lateral angles 

 very acute. 



Remarks. — This desmid was first figured by the late Prof. Baik^y in his Micro- 

 scopical Observations (Smithsonian Contributions), as M. iucisa of Ktz., and Ra- 

 benhorst, in his Flora Europaea Algarum, confirms this identification. He has 

 probably, however, never seen the plant itself, but merely accepts the opinion of 

 Professor Bailey. Mr. Archer (Pritchard's Infusoria), thinks the American plant 

 is certainly distinct from the European, and this seems to me correct. The points 

 of difference are — the American form is nearly twice the size of the European, the 

 sinuses are much more widened outwardly, and the lobes are reduced rapidly in 

 breadth to a mere point at the end, the dorsum of the distal lobes is also, I believe, 

 more rounded. In his description of T. Americanum, as he calls it, Mr. Arclier 

 states the end lobe has its angles bidentate. In the only specimen I have seen, 

 the angles end in a very sharp, almost spine-like point. Dr. Leidy found the spe- 

 cies abiuidantly at Newport, Rhode Island, and his figure agrees with mine in this 

 respect. In regard to the name, as there is already an M. Americaniim, the specific 

 name of Archer cannot be adopted, and for a similar reason it would not do to call 

 it 31. BaiJeyi. I have then been forced to give it a new title. 



Fig. 4, pi. 13, was drawn by myself from the single specimen I have seen; fig. 

 4 a was drawn by Dr. Leidy from a Newport specimen. 



M. oscitans, Ralfs. 



M. magna, poena tarn longa quara lata, subpinnatisecta, a vertice elliptico fusiformis, utroque 

 polo bifida; lobis basalibus horizontalibus conico-productis, apice bilidis; labo polari a lobis 

 basalibus sinu aniplo ac rotundato disercto, plus minus cnnvexo, haud raro truncato, rarius 

 leviter retuso, utririque producto acuminato, plerumque bidentato. (R.) 



