142 FRESH-WATER ALGiE OF THE UNITED STATES. 



Segments three-lobed, basal lobes long, subconical, acute ; termina. lobes slender, forked at the 

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



M. qnadrata, Bailiit. 



M. arcuatae similis, sed duplo major, semicellularum lobi basales minus arcuati, basi inflati, 

 apice bidentati et cytioderma irregulariter granulatum. (R.) 



Biam.—0. 0043"— 0.0049". 



Syn. — M. quadrata, Bailet, Microscopical Observations : Smithsonian Contributions, vol. ii. 

 Large quadrangular, three-lobed, basal lobes elongated, slightly curved, bidentate ; terminal 

 lobes with two slender transverse bidentate projections. Bailey. 



TH. disputata, Wood. 



M. magna, fere tarn longa quam lata, subpinnatiseeta, sinu acuto, lobis sequalibus ; semieellulis pro- 

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

 dilatato, dorso rotundato, angulis lateralibus acutissimis. 

 Long- t! J/ =-005". Lat. ^1?/ = -004". 



Syn. — Micrasterias incisa, Ktz. Bailey, Microscopical Observations : Smithsonian Contribu- 

 tions, 1850. 

 Hand Micrasteria incisa, KiJTZiNG, Spec. Algarum, p. IH. , 



Tetrachastrum Americanum, Archer, Pritchaed's Infusoria, 1860, p. ^25. 

 Hob. — South Carolina; Georgia; Florida; Rhode Island ; Bailey. Pennsylvania; 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. Bailey in his Micro- 

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

 benhorst, in his Flora Europsea 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. Archer 

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

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

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

 it M. Baileyi. 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, psene tam longa quam lata, subpinnatiseeta, a vertiee elliptieo fusiformis, ntroque 

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

 basalibns sinu amplo ac rotundato discreto, plus minus convexo, baud raro truncato, rarius 

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



