F R E S II -W A T E R A L G yE OF THE UX T EI D ST AT E S. 109 



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

 jugation in this species diifers from that in the rest of this genus; for, as in ////«- 

 lotheca (lissiliens, 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, Ralfs. 



P. cellulis anguste lauceolatis, diametro inaximo 5-6 plo longioribus, a medio in apices subtran- 

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

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



Dmw!.— 0.00159"— 0.00175". (R.) 



Syn. — P. closterioides, Ralfs. Rabeniiorst, 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 subtruucate apices; chloruphyl lamina deep green, interrupted by a median 

 pale band. 



Genus CLOSTERIUM, Nitsch. 



Cellulae interdum cylindricae sed saepius fusiformes et utroque polo attennatas, plus minus lunula- 

 tim curvatfe, in medio hand constrictae sed stria transversa uniea vel 2-5 impresste. Cytioderma 

 tenue, sat firmum, \seve vel plus minus distincte striatum et interdum longitudinaliter costatum. 

 Cytioplasma chlorophyllosa plerumque in lamiuis longitudinalibus disposita, et sub cellulae polis 

 loeello achroo, plerumque globoso et corpusculis plus minus numerosis se vivide movcntibus inipjeto 

 iustructa. 



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 striaj. Cytiodcrm 

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

 Chlorophyllous cytioplasra 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 cori)uscles. 



a. Zijgosporae globosx, rarissime angulares ; cellulae crura aut non aut minus producfa. 

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

 duced. 



1. Cellulse cylindricse, ad utrumque polum vix vel paulluvi attenuate, rectae vel leviler curvalae, 

 apic'ibus rotundatis vel truncalis. 



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

 curved, the apex rounded or truncate. 



C striolatuin, Ehrb. 



C. anguste lanccolato-fusiforme, leviter arcnatnm, 8-12 plo fere longius qnam latum, utroqne 

 polo paulum sensimqne attenuatum, apicibus truncatis saepo fuscescentibus ; mcmbrana dis- 

 tinctissime striata, vacuata fusceseente; vesiculis chlorophyllaceis 5-7 (in quoque crure) ; 

 loeello apices versus sito, submagno, corpuscula 12-20 includentc. (R.) 



Dia7n._J5"— 5V' = 0.00152"— 0.00187". (R.) 



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



Hab. — In aquis quietis. Centre County, Pennsylvania. Wood. Saeo Pond, New Ilampshire. 



(Lewis) . 

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



