FRESH-WATER ALG^ OP THE UNITED STATES. 145 



country, but I have never met with it. All the specimens which have come under 

 my notice were obtained in " Shepherd's Dam," near Greenwich, Cumberland 

 County, New Jersey. None of them were as large as the maximum of the European 

 measurements of which Rabcnhorst gives 0.0109" as the diameter. 



Fig. 5, pi. 13, represents a frond of this species, magnified 260 diameters. 



M. denticiilata, Breb. ? 



M. permagna, paulo longior quam lata, Ijevis; semicellulis quinquelobis (psene 9 lobis) ; lobis 

 intermediis et basalibus simillimis, bilobatis, lobulis item in lobulis bifulis duobus divisis ; 

 lobo polare angusto, cuneato, in apice plus minus iuciso ; margine minute deuticulato. 



Biam.— hat .0092". Long. .011." 



Syn. — 31. denticulata, Brebisson. Ralfs, British DesmidicEe, p. 70, et Archer, Pritchard's 

 Infusoria. 

 M. denticulata, Brebisson. ? Rabenhorst, Flora Europ. Algarum, Sect. III. p. 192. 



Hab. — Pennsylvania; Wood. Florida; Bailey. 



Very large, a little longer than broad, smooth; semicells with five lobes (scarcely 9); basal 

 and intermediate lobes alike bilobate, lobules also divided into two bifid lobules; end lobe 

 narrow, wedge-shaped, more or less incised at its apex ; margin minutely denticulate. 



Remarlis. — Prof. Rabenhorst gives M. denticulaia, Breb. as merely a variety of 

 M. furcata, Ac, stating that it only differs from the latter in the marginal incisions 

 and teeth. Not having access to the original description of Brebisson I cannot 

 express an opinion as to whether Prof R. is correct or not, but the specimen from 

 which the above description was drawn up (and which is figured on plate 13) cer- 

 tainly differs from M. furcata very essentially in the arrangement of its lobes, and 

 is, I feel confident, M. denticulata, Breb. of Ralfs and Archer. 



Fig. 6, pi. 13, is a drawing of this plant, as seen by myself, magnified 260 

 diameters. 



I?I. radiosa, Aa. 



M. maxima, orbicularis, Ifevis, anteccdonti simillima, differt inprimis scgmentis ultimis tumidis 

 in apicera bi- tri- fidura attenuatis, lobo polari vix prominulo, apice siuuato, ad utrumque 

 angulum bi- tri- dentato. (R.) Species mihiignota. 



DiOOT.— 0.0016". (II.) 



Syn. — M. radiosa, Agardh. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 192. 



Sab. — Florida ; Bailey. 



Frond orbicular, smooth ; segments 5-lobed ; basal lobes twice, middle lubes generally thrice 

 dichotomous, ultimate subdivisions inflated, attenuate towards the end, bideutate; end lobes 

 emarginate, its angles dentate. (A.) 



m. fimbriata, Ralfs. 



M. magna, orbicularis, Isevis (nonnunquam superficie aculeis singulis sparsis) ; semicellulis 

 quinquelobis, lobis omnibus confertis, basalibus angustioribus, repetito bilobulatis, lobis inter- 

 mediis duplo latioribus, repetito-bilobnlatis, lacinulis extremis leviter emarginatis, in angulis 

 spinis elongatis armatis; lobo polari prominulo, in apice obtuse siniiato- vel- undulato-emar- 

 ginato, angulis lateralibus rotundatis, ad marginem superiorem spinis singulis vel gcminis 

 obsito (rarius nudo). (R.) Species mihi ignota. 



19 August, 1872. 



