108 FRESH-WATER ALG^ OP TEE UNITED STATES. 



Hab.—Souih Carolina; Florida. Bailey. Rhode Island. (S. T. Oluey) Thwaites. 



Froud .slender, .snture nut i)riiminent; segments four to six times longer than broad, somewhat 

 tapering, inlialiou obsolete, sides straight, ends entire; e. f. without puncture. L. ^jj''; 

 ii- izW- (Areher.) 



b. Cellulx in medio non constrictae. 



b. Cells not constricted in the middle. 



P. interriiptum, Breb. 



"P. eellulis late lineari-cylindricis, diametro 5-C plo longioribus, utroque polo subito euneato- 

 acutatis, apicibus obtuso-rotundatis; laminis chlorophjllaceis longitudinalibus saturate viridi- 

 bus, oetate provccta fasciis transversis tribus pallidis iuterruptis. " (R.) Species mihi ignota. 



X>iani.-0.0()147"— 0.001(7". (R.) 



Sijn. — P. inlerruptum, Bueb. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 119. 



Hab. — 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. Jeiiiieri, Ralfs. 



P. ab P. Brebissonii vix discernendum, eellulis cylindricis, utroque polo rotundatis, Isevibus, dia- 

 metro 2i-5 plo longioribus ; zygosporis plerumque globosis, membrana fuscesceute subgranu- 

 lata. (R.) Species mihi ignota. 



Z)mwi.—0.0005T"— 0.0006". (R.) 



Syn. — P. Jcnneri, R.alfs. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 120. 



Bab. — In fossis, Florida. Prof Bailey. 



Scarcely distinguishable from P. Brel)issonii, cells cylindrical, rounded at each end, smooth, 

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

 granulate. 



P. Brebissonii, (Mengh.) Ralfs. 



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

 cylindricis, interdum nonnihil curvatis sed pleruraque rectis, diametro 2i-4 plo longioribus, 

 utroque polo late rotundatis, in medio non coustrictis ; " zygosporis angularibus vel rotundatis, 

 membrana fuscente, .subtiliter granulata." 



.Viam.—jj%^" = .00066". 



Syn. — P. Brebissonii, (Mengh.) Ralfs. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 

 120. 



Hob. — In fossis. South Carolina. (Prof Ravenel.) 



In an indefinitely expanded mucous mass, intermixed with other algte ; 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. 

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

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

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

 however, Prof Ravencl's specimens are immature, 



