IM FRESH-WATER ALG^ OF THE UNITED STATES. 



Syn.-M. ringens, Bailey, Microscopical Observations, pi. 1, fig. 11: Smithsonian Contri- 

 butions, vol. ii. 



Hah Florida; Bailey. 



Oblong, segments three-lobed, coarsely granulated near the edge ; basal lobes subdivided by a 



deep notch into two rather broad and obtuse or slightly bidentate projections ; terminal lobes 



exserted, emarginate ; extremities bidentate or obtuse. 



* * Semicellulae quinque-lobaise. 



* * Semicells 5-lobed. 



in. truncata, (Coeda) Breb. 



M magna, orbicularis, aut laevis aut suhtiliter punctata ; semieellulis quinquelobis, lobis inter 



se Sinn obtusangulo subangusto discretis, basalibus et intermediis inciso-lobulatis, segmentis 



acute bidentatis; lobo polari late cuneato, in dorso truncato, modo leviter convexo, modo 



leviter retuso, angulis aut bidentatis aut integris. (R.) 



X»iam.— 0.003" Long. .0036". 



Syn.—M. truncata, (Coeda,) Beebisson. Rabenhoest, Flora Europ. Algarum, Sect. III. p. 



191. 

 J2"a6.— Georgia ; Florida; Rhode Island; Bailey. Pennsylvania; Wood. Rhode Island 



(S. T. Olney); Thwaites. 

 Frond orbicular, smooth ; segments 5-lobed ; basal and middle lobes obscurely bipartite, ex- 

 tremities bidentate ; end lobe very broadly cuneate, bidentate at the angles, and with a slightly 

 central concavity. (A.) 



Remarks. — The dimensions. given above were taken from the largest specimens 

 I have seen, but do not at all equal those given^ by Prof. Rabenhorst, his breadth 

 is .0011". According to the same authority, M. crenata, Breb,, is merely a variety 

 of this species. 



Fig. 15, pi. 21, represents the outline of a frond of this plant. 



M. fnrcata, Aa. 



M. permagna paulo longior quam lata, levis ; semicellulis quinque lobis (psene T-lobis) ; lobis 

 omnibus rectis ; lobis basalibus angustioribus, bilobulatis, lobulis bifidis, sinu obtusangulo 

 vel acutangulo, segmentis linearibus bidentatis (denticulis s^pe inaequilongis) ; lobis inter- 

 mediis duplo latioribus, inciso-bilobis, lobulis iisdem ac loborum basalium ; lobo polari non- 

 nihil anguste cuneato, prominulo, in apice plus minus profunde sinuato-vel undulato incise, 

 angulis bidentatis. 



Diam.— ylSV = .008". 



Syn. — M. rotatw, Ralps, British DesmidicEe, p. 11. 



M. furcata, Agaedh. Rabenhoest, Flora Europ. Algarum, Sect. III. p. 191. 



Hob. — South Carolina; Georgia; Florida; Rhode Island ; Bailey. New Jersey; Wood. 



M. very large, a little longer than broad, smooth ; semicells 5-lobed (scarcely 7-lobed) ; lobes 

 all straight ; basal lobe narrower than the intermediate, bilobulate, lobules bifid, their sinuses 

 acute or obtuse, segments linear, bidentate ; teeth often long and unequal ; intermediate lobes 

 twice as wide as the basal, bilobate, their lobules of the same form as the basal lobe ; end 

 lobes narrowly cuneate, prominent, more or less profoundly sinuately or undulately cut at 

 the apex, angles bidentate. 



RemarJcs. — According to Eabenhorst and others, there is a European form of 

 this species in which the marginal teeth are wanting. This may exist in this 



