1839.] 1^^ [Wood. 



wards firm, tubercular, deep olive greeu : cells globose or elliptical ; in 

 tlie immature thallus, single or geminate, frequently scattered ; in the 

 mature thallus often closely conjoined into families, mostly crowded ; in 

 the young thallus the teguments of the cells are mostly diffluent, after- 

 wards distinct. 



Diam. cell. glob. max. 3^^^"=. 00028 ; cell, oblong, long. max. ^sW 

 =.0004. 



GEN. TETRASPOEA. 

 T. LTJBRICA. {Roth) Ag. 

 In aquis limpidis prope Philadelphia. 



GEN. RHAPHIDIUM. 

 R. POLYMORPHUM. Fveseii. 

 Hab. Pi'ope Philadelphia. 



FAM. PROTOCOCCACEAE. 



GEN. SCENESDESMUS. 

 s. ACXJTUS. Meyen. 

 Hab. Prope Philadelphia. 



S. POLYMORPHUS. 8p. NoV. 



S. cellulis fusiformibus, aut ovalibus aut ellipticis aut globosis, sin- 

 gulis aut 2-8 conjunctis, plerumque utroque polo aculeo unico, interdum 

 aculeis duobus, instructis : apicibus obtusis, acutis, vel acutissimis ; 

 aculeis gracillimis, rectis, modice elongatis, inclinatis. 



S. cells fusiform, or oval, or elliptic, or globose, single or 2-7 con- 

 joined, furnished in most cases with a single spine, sometimes 2, at each 

 end ; ends obtuse, acute or very acute ; sijines exceedingly slender and 

 acute, straight, moderately long, inclined. 



Diam. ^^^^"-^J-^-^" ; plerumque ^oVo"- 



Hab. In aquis quietis prope Camden, New Jersey. 



GEN. HYDRODICTYIOK 



H. trTRICtJLATUM. Roth. 



Hab. In stagnis prope Philadelphia. 



GEN. PEDIASTRUM. 



B. BORYANTJM. {Titrpin.) Mengh. 

 Hab. In stagnis prope Philadelphia. 



A. P. S. — VOL. XI — R 



