FRESH -WATER ALG^ OF THE UN T BID STATES. 109 



Mr. Ealfs' description of the conjugation is as follows : The process of the con- 

 jugation in this species differs from that in the rest of this genus; for, as in Hya^ 

 loiheca dissiliens, the conjugation cells enter into the formation of the containing 

 cell and are permanently attached to the sporangium, instead of being detached, 

 as commonly happens, in the Desmids. The sporangium is at first cruciform, then 

 quadrate, and finally orbicular. 



P. closterioides, Ralfb. 



P. cellulis anguste lanceolatis, diametro maximo 5-6 plo longioribus, a medio in apices subtrun- 

 cato-rotundatos sensim attenuatis ; laminis chlorophyll, saturate viridibus, medio fascia trans- 

 versa pallida interruptis. (R.) Species mihi ignota, 



Dtam.— 0.00159"— 0.00175". (R.) 



Syn. — P. closterioides, Ralts. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 121. 



Hab. — Prope Grahamsville, South Carolina. Prof. Bailey. 



Cells narrowly lanceolate, 5-6 times longer than the greatest diameter, sensibly attenuate from 

 the middle into the subtruncate apices ; chlorophyl lamina deep green, interrupted by a median 

 pale band. 



Genus CLOSTERIUM, Nitsch. 



Cellulae interdnm cylindricse sed saepius fusiformes et utroque polo attenuatae, plus minus lunnla- 

 tim curvatse, in medio hand constrictse sed stria transversa unica vel 2-5 impressse. Cytioderma 

 tenue, sat firmura, Iseve vel plus minus distincte striatum et interdum longitudinaliter costatum. 

 Cytioplasma chlorophyllosa plerumque in laminis longitudinalibus disposita, et sub eellulse polis 

 locello achroo, plerumque globoso et corpusculis plus minus numerosis se vivide moventibus impleto 

 instructa. 



Cells sometimes cylindrical, but more often fusiform and attenuate at each end, more or less 

 Innately curved, in the centre not constricted but marked with from 1-5 transverse striae. Cytioderm 

 thin, moderately firm, smooth or more or less distinctly striate, and sometimes longitudinally costate. 

 Cblorophyllous cytioplasm mostly arranged in longitudinal lamina, and furnished at each end with a 

 clear space, which is mostly globose, and contains more or less numerous actively moving corpuscles. 



a. Zygosporse glohosse, rarissime angulares ; eellulse crura aut non aid minus producta. 



a. Zygospores globose, very rarely angular; crura of the cells not at all, or only slightly, pro- 

 duced. 



1. Cellulee cylindricee, ad utrumque polum vix vel paullum attenuatae, rectse vel leviter curvatse, 

 apicibus rotundatis vel iruncatis. 



1. Cells cylindrical, not at all or but slightly attenuated at the ends, straight or slightly 

 curved, the apex rounded or truncate. 



C. striolatum, Ehrb. 



C. anguste lanceolato-fusiforme, leviter arcuatnm, 8-12 plo fere longius quam latum, utroque 

 polo paulum sensimque attenuatum, apicibus truncatis saepe fuscescentibns ; membrana dis- 

 tinctissime striata, vacnata fuscescente; vesiculis chlorophyll aceis 5-7 (in quoque crure); 

 locello apices versus sito, submagno, corpuscula 12-20 includente. (R.) 



Diam—sV'— ?V'= 000152"— 0.00187". (R.) 



Syn.—G. striolatum, Ehrb. Rabenhorst, Flora Europ. Algarum, Sect III. p. 125. 



Hab.— In aquis quietis, Centre County, Pennsylvania. Wood. Saco Pond, New Hampshire. 



(Lewis) 

 Narrowly lanceolately-fusiform, slightly bent, 8-12 times longer than broad, sensibly attenuated 



