118 FRESH-AVATEll AL(J.E OF THE UNITED STATES. 



T. levis, (KuTZ.) Ralfs. 



T. Bivbissouii forrais similis sed parvior, 3-4 i)Io longior quam latiis ; cytiodermate plerumque 



levissimo, interdum iudistiuclissiiue juiuetato. 

 D/am.—x5V/ = . 00066". 



Syn. T. levis, Kutzing. Ralfs. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 140. 



ffah. — In aqui.s quietis, propo Philadelphia. 



Similar in form to T. Br^bissonii, but smaller, 3-4 times longer than broad ; cytioderm mostly 

 very smooth, sometimes iiulistiiictly punctate. 



Remarks. — Prof. Kabeiihorst states that the cytioderm of tliis species is very 

 smooth, and Mr. Ralfs says that he has failed to detect any punctations, but also 

 states that " Mr. Jenner and Mr. Ross assure me that they (punctae) are scattered 

 as in T. grcmnlaius." I have no doubt of their existence in certain individuals, 

 whilst in other cases they appear to be absent. 



Genus PLEUROT^NIUM, N^geli (1849). 



Cellulte singuliE in aqua natantes, rectoe vel subrectae, eylindricse vel fusiformes, valde elongataB, 

 utroque polo rotundatas vel truncatoe, medio leviter constriotse, ex transverso circulares. Cytio- 

 plasma chlorophyllaccum in laniinis longitudinalibus pluribus dispositum, et sub utroque polo locello 

 rotundato corpuseulis se vivide moventibus impleto instructum. 



Cells single, swimming in water, straight or nearly so, cylindrical or fusiform, very much elongate, 

 rounded or truncate at each end, in the end view with a circular outline. Chlorophyllous protoplasm 

 arranged in longitudinal lamince and furnished at each end with a round vacuole containing actively 

 moving corpuscles. 



EemarTcs. — This genus appears to include the main portion of the species, which 

 have been described under the name of Docid'mm ; the remainder being represen- 

 tatives of a number of genera. I have not had access to the original description 

 of Docidium, and do not know in what year it was published ; but, according to 

 De Bary, Docidium is much the older name ("Ucber de Conjugat.," p. 75). M. 

 De Bary states, however, that he prefers the name of Ntegeli, because that autho- 

 rity first defined the genus and his name expresses very clearly the character 

 of it, as well as from the circumstance that the name Docidium having been 

 made to cover a lietcrogcncous mass of species, its retention might cause confu- 

 sion. I confess to thiidving that this action of De Bary is not in accordance with 

 the recognized laws of priority, but, in the absence of the original description, 

 have thought best to follow it. 



P. trabeciila, (Ehrb.) Njegeli. 



P. ssepe valde clongatum, octies vicies-longius quam latum, cylindraceum, utroque fine h-evissimo 

 attenuatum aut incrassatum, juxta medium constrictum ssepius bigibbum (quasi biundatuin), 

 apicibus late truncatum ; cytiodermate tenui loevi, achroo. (R.) 



X)ja?H.— 7^/ = .0013". 



Syn. — " Docidium Ehrenbergii. Ralfs." Bailey, Microscopical Ob.servations. Smithsonian 

 Contributions. 



Pleurotamium (rabecula, (Ehr.) N^oeli. Rabenhorst, Flora Europ. Algarum, Se^t. 

 III. p. 141. 



.ffa&.— South Carolina, Georgia, Florida ; Bailey. Pennsylvania ; Wood. 



