FRESH-WATER A L G yE OF THE UNITED STATES. 85 



outer coat. The lateral transparent spot in the cells is mostly very evident, some- 

 times it is wanting, however. Occasionally there is a very distinct blackish " eye 

 spot." The threads which join the cells are very delicate, and I have never been 

 able to absolutely demonstrate their meeting in the centre of the frond, although 

 I believe they do so. In mounted specimens, even when preserved in carbolic 

 acid water, they disappear after a time. I have never seen zoospores or any other 

 reproductive bodies. 



Genus RHAPHIDIUM, Ktz. 



Cellulae fasiformes vel cylindracefe, ntrinque (plerumque) sensim sensimque cuspidatae vel acunii- 

 natce, rarius obtusatae, rectse vel varie curvatae, singulis, geminse vel fasciculatim aggrcgatae, medio 

 decussatim vel radiatim coujunetae, rarius binae sub polls lateraliter connesae, ceterum liberse. 

 Cytioderma tenue, laeve. Cytioplasma viride, subtiliter granulosum, locello pallidiori vel acliroo, 

 centrali, rarius lateral!, praeditum. Cellularum divisio ad unam directionem. (R.) 



Cells fusiform or cylindrical, generally very gradually cuspidate or acuminate at the ends, rarely 

 obtuse, straight or variously curved, single, geminate, or fasciculately aggregate, decussate in the 

 centre or radiately conjoined, rarely two laterally united at the end, other cells free. Cytioderm 

 thin, smooth. Cytioplasm green, very finely granular, furnished with a central or rarely lateral 

 transparent vacuole. Division of the cells occurring only in one direction. 



R. polj'inorphiiin, Fresen. 



R. cellulis rectis vel varie curvatis, singulis, vel 2-4-8-16 fasciculatim collocatis, gracilibus, 

 saepe graeiliimis, nonnunquara medio paulium turgidis, subventricosis, nonnunquam paullum 

 constrictis, apices versis, sensim atteuuatis, acutissimis. 



Z)iam.— 7 jVo" =-00013". 



Syn.—B. polymorphum, Fresen., Rabenhorst, Flora Europ. Algarum, Sect. III. p. 44. 



Jjab. — Prope Philadelphia, Wood. 



Cells straight or variously curved, single or 2-4-8-16 fasciculately joined together, slender, 

 often exceedingly so ; sometimes slightly turgid in the centre, subventricose, sometimes 

 slightly constricted ; the apices gradually attenuate, very acute. 



Var. falcatiim. 

 Cellulis fusifurmibus, gracillibus, utroque fine acutissime cuspidatis, curvatis vel semilunaribus, 

 4-16 fasciculatim cougregatis. 



Syn. Ankisirodesmys falcatus. (Corda.) Rabenhorst, Flora Europ. Algarum, Sect. III. 



p. 45. 

 Hah. — South Carolina, Georgia, Florida, Rhode Island. (Bailey.) 



Cells fusiform, slender, at each end very acutely cuspidate, cijrved or semilunar, 4-16 fascicu- 

 lately congregate 



Remark. — Fig. 3, pi. 7, represents different forms of E. polymorphum. 



Family PROTOCOCCACE^. 



Algae unicellulares sensu strictissirao, chlorophyllosae, et vegetatione terminali et ramificatione 

 vera carentes, sine cellularum generatione vegetativa. Vivnnt aut singulae, segregatae aut in fami- 

 lias consociatae. Harum familiarnm cellulae nuraero aut indefinitae .semper ,se angente.s (turn sensu 

 vero familiffi nonien ferunt), aut definitoe, se non augentes (quae coenobiura dicuntur). 



