108 FRESH-WATER A L G M OF THE UNITED STATES. 



Hob. South Carolina; Florida. Bailey. Rhode Island. (S. T. Oluey) Thwaites. 



Frond slender, suture not prominent; segments four to six times longer than broad, somewhat 

 tapering, inflation obsolete, sides straight, ends entire; e. f. without puncture. L. 5^2' > 

 B. T5 W- (Archer.) 



6. Cellulse in medio non constrictae. 



b. Cells not constricted in the middle. 



P. interrnptam, BREB. 



"P. cellulis late lineari-cylindricis, diametro 5-6 plo longioribus, utroque polo subito cuneato- 

 acutatis, apicibus obtuso-rotundatis ; laminis chlorophyllaceis longitudiualibus saturate viridi- 

 bus, astate provecta fasciis transversis tribus pallidis interruptis." (R.) Species mihi ignota. 



Diam.-O.QOUr 0.00177". (R.) 



Syn. P. interruptum, BREB. RABENHOEST, Flora Europ. Algarum, Sect. III. p. 119. 



Hob. In fossis, South Carolina, prope Grahamsville. Prof. Bailey. 



Cells broadly linearly cylindrical, 5-6 times longer than broad, at each end suddenly cuneately 

 sharpened, the apex obtusely rounded ; longitudinal chlorophyl lamina deep green, in ad- 

 vanced age interrupted by three transverse pale fascia. 



P. Jenneri, RALFS. 



P. ab P. Brebissonii vix discernendam, cellulis cylindricis, utroque polo rotundatis, lasvibus, dia- 

 metro 2^-5 plo longioribns ; zygosporis plerumque globosis, membrana fuscescente subgranu- 

 lata. (R.) Species mihi ignota. 



Diam. 0.00057" 0.0006". (R.) 



Syn. P. Jenneri, RALFS. RABENHOKST, Flora Europ. Algarum, Sect. III. p. 120. 



Hab. In fossis, Florida. Prof. Bailey. 



Scarcely distinguishable from P. Brebissonii, cells cylindrical, rounded at each end, smooth, 

 2^-5 times longer than broad; zygospores mostly globose, membrane somewhat fuscous, sub- 

 granulate. 



P. Brebissonii, (MENGH.) RALFS. 



P. in massa mucosa indefinite expansa saepe cum algis alteris intermixtis; cellulis perfecte 

 cylindricis, interdum nonnihil curvatis sed plerumque rectis, diametro 2^-4 plo longioribus, 

 ntroque polo late rotundatis, in medio non constrictis ; " zygosporis angularibus vel rotuiidatis, 

 membrana fuscente, subtiliter granulata." 



. 7i V = .00066". 



Syn. P. Brebissonii, (MENGH.) RALFS. RABENHORST, Flora Europ. Algarum, Sect. III. p. 

 120. 



Hab. In fossis, South Carolina. (Prof. Ravenel.) 



In an indefinitely expanded mucous mass, intermixed with other algae; cells perfectly cylindri- 

 cal, sometimes slightly curved, but generally straight, at each end broadly rounded, not con- 

 stricted in the middle ; " zygospores angular or rounded, membrane fuscous, finely granu- 

 late." 



Remarks. Among the numerous desmids which I have received from Prof. 

 llavenel are some which, I think, must be referred to P. Brebissonii, although they 

 do not nearly equal the size of the European form, nor even the diameter given 

 above, which is almost the lowest limit of the mature foreign plant. I believe, 

 however, Prof. Ravenel's specimens are immature. 



