FRESH-WATER A L G vE OF THE UNITED STATES. 127 



Cells 3-4 angular or compressed, not constricted, tbeir lateral margins plain or crenate, conjoined 

 into angular perforately articulate fascia. 



A. Baileyi, Ralfs. 



" Filament not crenated ; joints about equal in length and breadth. 



Si/n. — Odontella? tridentata, Bailey. In lit. cum icone (184G). 



Jjab. — Worden's Pond, Rhode Island; near Princeton, New Jersey, with sporangia," Bailey. 



" Filament triangular; joints excavated at their junction like those of Aptogouum desmidiuiii- 

 The joints are not bicrenate, hence the margins of the filament are entire, a character which 

 distinguishes it from that species. The end view is triangular, with rounded angles." Ralfs, 

 British Desmidiese, p. 208. 



Genus COSMARIUM, (Coeda) 



Cellulse oblongaB, oblougo-cylindricse, ellipticce, vel orbiculares, medio transverse plus minus con- 

 striciE, utroque polo obtusai vel rotundatse et Integra!, a vertice ellipticaj. Zygospora; muricata; vel 

 verrucosse. 



Cells oblong cylindrical, elliptical or orbicular, more or less transversely constricted in the middle, 

 obtuse or rounded, and entire at each end, viewed from the end elliptical. Zygospore warty or 

 muricate. 



1. Cellules sejunctee. 



1. Cells seijarate. 



a. Cellulae ellipticse, vel suhellipticse ; semicellulse medio nonvenlricosae. 



a. Cells elliptical or subellipitical ; semicells medianly not ventricose. 



* Gytiodermate granidoso vel verrucidoso. 



* Cytioderra granular or warty. 



C inni'grarifireriiin, (Turp.) Mengh. 



C. paulo longius quam latum, profunde constrictnm ; sinu amplo, vel modice angusto, interdum 

 intra e.xcavato; semicellulis semiorbicularibus, vel reniformibus vel nonnihil quadrangulis 

 dorso plerumque late rotundatis ; cytiodermate verruculoso. 



Z>w?Ji.— Max. ^5V = .0006" (0.00073"— 0.0012". R.) 



Syn. — Euastrum margaritiferum, I^hrb. Bailey, Silliman's Journal, 1841. 



Cosmarium margaritiferum (Turpin), Meneghini. R.\isenuorst, Flora Europ. Algar., 

 Sect. III. p. 157. 



Eab. — In aqnis quietis, South Carolina ; Florida ; Mexico ; Bailey. Pennsylvania, Wood. 



A little longer than broad, profoundly constricted ; sinus ample or moderately narrow, some- 

 times widened on the inside; semicells seniiorbicular, reniform or somewhat quadrangular ; 

 dorsum mostly broadly rounded ; cytioderm warty. 



Remarhs. — I have found a form of this species growing in the vicinity of this 

 city, which I at first was disposed to look upon as distinct, but which, in truth, 

 grades into the typical form. In it the cells are almost quadrangular, often with 

 their basal angles acute. The margin of the frond in C. mar<jar'diferum, as it 

 occurs with us, is sometimes distinctly serrate or, more correctly, crenulate from 

 the presence of the granulations. The granules are larger than in C. hoirytis, but 

 smaller than in C. tetroi>htltalmvm. When viewed laterally the semi-cells are 

 roundish, or nearly so (according to Ralfs' elliptical), and closely connected by 



