FRESH-WATER ALG^ 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 EHAPHIDIUM, Ktz. 



Cellulse fusiformes vel cylindraceae, utrinque (plerumque) sensim sensimque cuspidatse vel acumi- 

 natae, rarius obtusatse, rectae vel varle eurvatse, singulae, geminse vel fasciculatim aggregatse, medio 

 decussatim vel radiatim conjunctsB, rarius binae sub polls lateraliter connexae, eeterura liberae. 

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

 central!, rarius laterali, praeditum. Cellularum divisio ad unam direetionem. (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. pol^morphnm, Fbesen. 



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

 saepe gracillimis, nonnunquam medio paullum turgidis, subventricosis, nonnunquam paullum 

 constrictis, apices versis, sensim attenuatis, acutissimis. 



I)iam.—js\^" = .00013". 



gyn. — B. polymorphum, Fresen., Rabenhorst, Flora Europ. Algarum, Sect. III. p. ii. 



ffab. — 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. falcatum. 

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

 4-16 fasciculatim congregatis. 



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



p. 45. 



^£j5. — South Carolina, Georgia, Florida, Rhode Island. (Bailey.) 



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

 lately congregate 



Bemarh. — Fig. 3, pi. T, represents different forms of R. pdlymorphum. 



Family PEOTOCOCCACE^. 



Algae unicellulares sensu strictissimo, chlorophyllosae, et vegetatione terminali et ramifieatione 

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

 lias consociatae. Harum farailiarum cellulae numero aut indefinitse semper se augentes (turn sensu 

 vero familiffi nomen ferunt), aut definitae, se non augentes (quae coenobium dicuntur). 



