Desmidieiv ] iNFUsoRrAL animalcules. 217 



by the presence of processes, which, unlike those in the other species, 

 do not diverge in the front view, but spread laterally, in such a manner, 

 that the one nearest the eye, more or less conceals its companions. 



MicRASTEEiAS BaUeyi. — Granulated ; segment three-lobed ; lobes 

 bipartite, end one much exserted ; all the sub-divisions bidentate at 

 the apex. 



M. incisa = Euastrum crux-melitennis, (Ehr.) — Lobes horizontal, 

 basal ones tinmcate, with a tooth at each angle ; end lobe convex, its 

 angles acute. 



The following new species are foimd in the Southern States of 

 America, and were discovered by Dr. Bailey of New York in 1850. 



M. arcuata, (B.) — Quadrangidar segments three-lobed, the basal 

 lobes long and arcuate, subtended by the transverse projections 

 from the ends of the slightly notched terminal lobes. An interesting 

 and very distinct species, which can be confounded with no other 

 except the following. Lakes in Florida. 



M. expansa, (B.) — Segments three-lobed, basal lobes long, sub- 

 conical, acute ; terminal lobes slender, forked at the end, with the 

 divisions much shorter than the basal lobes. This somewhat re- 

 sembles the preceding species with which it occurs, but I have seen 

 no intermediate forms, out of many hundreds of each, and the cha- 

 racters above given appear sufficient to separate them. 



M. quadrata, (B.) — Large, quadrangular, 3-lobed, basal lobes 

 elongated, slightly cmwed, bidentate ; terminal lobes with two slender 

 transverse bidentate projections. Its larger size, and distinctly 

 bidentate projections, sufficiently distingmsh it from the two preceding 

 species. 



M. ringens, (B.) — Oblong, segments three-lobed, coarsely granulated 

 near the edge ; basal lobes sub-divided by a deep notch into two, 

 rather broad and obtuse, or slightly bidentate projections ; terminal 

 lobes exserted, emarginate; extremities bidentate or obtuse. Re- 

 sembles M. Baileyi, but is larger, divisions less slender, and with the 

 granulations differently placed. 



Genus Euastrum. — Frond simple, compressed, deeply divided into 

 two segments which are emarginate at their ends, lobed or sinuated, 

 generally pyramidal and ftimished with circular inflations. 



In Euastrum, Ehrenberg includes Micrasteaias (Agardli.) not 

 Micrasterias, (Ehr.) and Cosmariwn ; Euastrum agrees with Mtcras- 



