FRESH-WATER AhQM OF THE U:NITED STATES. 211 



£ra6.— South Carolina ; (Ravenel) Wood. Rhode Island; (S. T. Olney) Thwaites. 



Thallus linear, flattish, of half to a whole thumb's breadth, sometimes greatly elongate, bright 

 or obscure green, dichotomously subretieulately laciuiate (sometimes with the habit of 

 Riccia fiuitans) ; filament and primary branches mostly colorless, sometimes zoned with green, 

 parallel ; lateral fasciculi of branches more or less dense, divaricately patent ; joints more or 

 less tumid, diameter equal or subequal ; joints constricted ; cytioplasm effused granulate. 



Eemarks. — I have never seen a living or well-preserved specimen of this species, 

 and have, therefore, here simply copied the description of Prof. Eabenhorst. Prof. 

 Eavenel has sent to me dried algse labelled, and I think correctly, as belonging to 

 this species, but their condition did not allow any scientific study of them. 



Genus PILINIA, Ktz. 



Fila articulata, erecta, simplicia vel dichotome ramosa, basi afSxa, in stratum crustaceura sub- 

 spongiosum, fragile aggregata. Propagatio adhuc ignota. 



Filaments articulate, erect, dichotomously branched, fixed by the base, aggregated into a some- 

 what spongy fragile crustaceous stratum. Method of propagation unknown. 



P. diluta, Wood, (sp. nov.) 



P. rupicola, in strato cano-viridi disposita ; fills ramisque fasciculatis, apice obtusis ; articulis 

 diametro IJ plo-3j plo longioribus. i 



Diam. — Max. 0.0004". 



Hab. — In fontibus maximis, prope Bellefonte, Centre County, Pennsylvania ; Wood. 



Growing on stones and rocks, forming a grayish-green stratum ; filaments and branches fasci- 

 culate, with the apices obtuse ; joints 1^-3|- times longer than broad. 



Eemarks. — Near Bellefonte, Centre County, Pennsylvania, there issues from the 

 limestone rocks the largest spring I have ever seen, giving rise to a creek-like tor- 

 rent, which, supplies the city with water, and passes on scarcely diminished in 

 volume. In this spring grows the curious algae under consideration, forming a 

 somewhat lubricous crustaceous and stony stratum on the stones and rocks in the 

 basin. This stratum is of a grayish-green color, and is quite friable, breaking in 

 the direction of the filaments with the greatest possible readiness. When placed 

 tinder the microscope it is seen to be composed of filaments whose course is a 

 direct one from the under to the upper surface. They are apparently rigid, pre- 

 serving their courses, and not being intermatted. They are composed of cylindri- 

 -sal, confervoid cells, and are dichotomously branched, and yet when viewed as 

 a whole the filament and its branches form a sort of fasciculus. The basal cell 

 or cells appear to be globular. When I collected this plant I was forced by cir- 

 cumstances to put the specimens in carbolic-acid water for future study, and, 

 therefore, I have had no opportunity of studying their method of reproduction. 

 t am not altogether satisfied in referring this plant to the Pilinia, and yet all the 

 most important of the characters given by Rabenhorst are preserved by it. It 

 certainly, however, differs very greatly from P. rimosa, Ktz. 



Genus APHANOCHtETE, Braun. 



Fila distincte articulata, prostrata, repentia, interdum in stratum irregulare plus minusve concreta; 

 ramnlis repentibus vel adscendentibus ; cellulis chlorophyllaceis, apice vel dorso setigeris. Propa- 

 gatio zoogonidiis. 



