FRESH-WATER ALG^ OF THE UNITED STATES. Ul 



latis, rotundatis vel sinuato- bi- tricrenatis ; lobo polari abbreviate late truncato, leviter emar- 

 ginato, angulis acutis lateraliter plus minus, porrectis ; cytiodermate subtilissime puactato. 



Syn. — U. binale, (Tuepin) Ralps, British Desmide*, p. 90. 



Sa&.— Florida; Bailey. Rhode Island, (S. T. Olney,) Thwaites. Pennsylvania; Wood. 



Frond very minute, scarcely twice as long as broad, oblong ; segments with their basal portion 

 either entire or bicrenate at the sides, slightly contracted beneath the ends ; ends dilated, not 

 protuberant beyond the angles, its central notch acute, broad ; tr. v. with two lateral infla- 

 tions, ends truncate, angles rounded. (A.) 



Remark.— Fig. 3, pi. 13, represents the front view of a frond, magnified 750 

 diameters. 



Genus MICRASTERIAS, Ag. (1827). 



Cellulfe compressae, profunde constrictse, a fronte orbiculares vel late ellipticsB, a vertice fusiformes 

 cum utroque polo aeuto, semicellulse tri- vel quinque-lobae ; lobi basales aut integri aut pluripliciter 

 ineiso-lobulati; lobus polaris aut integer aut sinuatus aut emarginatus, et interdum angulis produe- 

 tus et bifidus. Cytioplasma chlorophyllacea in cellulae lumen subaequaliter distributa, granula 

 amylacea sparsa involvens. Cytioderma plerumque laeve, nonnunquam pnnctatum, granulatum vel 

 mucronatum'. 



Zygosporse globosas, setate provecta aculeis simplicibus, apice bi- multi- fidis, nonnunquam repetito- 

 multifiidis armatae. 



Cells compressed, profoundly constricted, viewed from the front orbicular or broadly elliptic,, from 

 the vertex fusiform with acute ends. Semicells 3- or 5-lobed ; basal lobes either entire or many 

 times incisely-lobulate ; end lobe either entire or sinuate or emarginate, and sometimes with its angles 

 produced and bifid. Chlorophyllous cytioplasm distributed nearly uniformly in the cavity of the 

 cell, surrounding scattered starch granules. Cytioderm mostly smooth ; sometimes punctate ; 

 granulate or mncronate. 



Zygospores globose, at maturity armed with simple spines, whose ends bifid or multifid, and some- 

 times repeatedly multifid. 



A. Semicellulse trilobse. Lobi basales horizontales ; lobus polaris valde dilatatus, dorso plane 

 convexus, truncatus vel leviter retusus, a lobis basalibus sinu amplissimo discretus. 



A. Semicells trilobate. Basal lobes horizontal ; end lobe strongly dilated, with the back con- 

 vex, truncate, or slightly retuse. 



M. arcaata, Bailet. 



M. mediocris, quadrangularis, paulo latior quam longa, profunde pinnatifida; lobis basalibus 

 angustis elongatis, arcuatis, in apicem acutum attenuatis, divergentibus ; lobis polaribus 

 angustusimis, utrinque graciliter productis, in apicem acutum attenuatis, in medio dorso 

 modice retusis. (R.) 



Syn. M. arcuata, Bailey, Microscopical Observations : Smithsonian Contributions, vol. iL 



Eab. — In stagnis. Florida; Bailey. 



" Quadrangular, segments three-lobed, the basal lobes long and arcuate, subtended by the trans- 

 verse projections from the ends of the slightly notched terminal lobes." (Bailey.) 



HE. expansa, Bailey. 



M. mediocris, tam longa quam lata, lobis stellatim expansis ; lobis basalibus angustis in apicem 



acutum attenuatis, divergentibus, rectis ; lobis polaribus e basi angusta sensim dilatatis, in 



medio dorso late sinuatis, angulis acutis (sed muticis). (R.) 

 8yn.—M. expansa, Bailey, Microscopical Observations : Smithsonian Contributions, vol. ii. 

 Eab. — In stagnis, Florida; Bailey. 



