FRESH-WATER ALG^ OF THE UNITED STATES. 127 



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

 into angular perforately articulate fascia. 



A. Bailey i, Ralfs. 



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



Syn. — Odontella? tridentata, Bailey. In lit. cum icone (1846). 



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



"Filament triangular; joints excavated at their junction like those of Aptogonum desmidium- 

 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 Besmidiese, p. 208. 



Genus COSMARIUM, (Coeda) 



Cellulae oblongse, oblongo-cylindricse, ellipticse, vel orbicnlares, medio transverse plus minus con- 

 stricae, utroque polo obtusse vel rotundatae et integrs, a vertice ellipticse. Zygosporae muricatae vel 

 verrueosse. 



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. Cellulae sejunctae. 



1. Cells separate. 



a. Cellulae ellipticse, vel suhellipticse ; semicellulae medio nonventricosae. 



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



* Cytiodermate granulosa vel verruculoso. 



* Cytioderm granular or warty. 



C. margaritiferum, (Turp.) Mengh. 



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

 intra excavato ; semicellnlis semiorbicularibns, vel reniformibus vel nonnihil quadrangulis 

 dorso plerumque late rotundatis ; cytiodermate verruculoso. 



X)iam.— Max. 35^%^'' = -0006" (O.OOO'TS"— 0.0012". R.) 



Syn. Euastrum margaritiferum, Ehrb. Bailet, Silliman's Journal, 1841. 



Cosmarium margaritiferum (Turpin), Meneghini. Rabenhorst, Flora Europ. Algar., 

 Sect. III. p. 157. 



Sab. In aquis 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 semiorbicular, reniform or somewhat quadrangular ; 

 dorsum mostly broadly rounded ; cytioderm warty. 



RemarJes.—l 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 G. margaritiferum, 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 G. hotrytis, but 

 smaller than 'm G. tetropUTialmvm. When viewed laterally the semi-cells are 

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



