FRESH-WATER ALG^ OP THE UNITED STATES 97 



What becomes of them after this, as has been stated, is a mere matter of conjec- 

 ture, M. Braun^ and others have described unicellular forms of several of the 

 multicellular species of Pediastrum, and Pringsheim suggests that these are really 

 polyhedrons developed out of these microgonidia, as is seen in the water-nets. 

 This, of course, may or may not be the case. 



P. Boryanum, (Tubfin) Mengh. 



P. coenobio orbiculari, oblongo vel elliptico, magnitudine vario, continuo, Isete viridi, e cellulis 

 4—8-16-32-64 (rarissime 128) composito (cellularum strato simplici, noDnunquam medio 

 duplicato) ; cellulis periphericis plus minus profunde emarginatis vel bilobis, lobis cornutis, 

 cornibus achrois hyalinis, abbreriatis vel elongatis, teretibus, obtusis vel subobtusis, interdum 

 capitellato-incrassatis, centralibus arctissime concretis, polygonis (4-6 angularibus), in antica 

 parte modo angulo prominulo modo plane truncatis, modo leviter repandis, omnium mem- 

 brana decussatim punctata. (R.) 



Diom.— Transv. cell 0.000T95"; rarius 0.00088"— 0.00094". (R.) 



Syn. — P. Boryanum, (Tuepin,) Menghini. Rabenhorst, Flora Europ. Algarum, Sect. III. 



p. T4. 

 Eab. — Georgia, Florida, Rhode Island, Bailey ; Pennsylvania, Wood. 

 Cells arranged in one or more circles round one or two central cells ; the inner variable, generally 



concave at one side, the outer tapering into two long subulate points, the notch narrow. 

 L. 1-2083" to 1-1633" ; B. 1-2733" to 1-2222". (Archer.) 



P. Selenaea, Ktz. 



P. coenobio orbiculari, integro, e cellulis 8-16 (rarius 31 = 1 -f- 5 + 10 -t- 15, Ktz.) formato; 

 cellulis periphericis angustis, lunatis, acute lobatis, disci cellulis leviter excisis, centrali unica 

 5-angulari, omnium membrana firma, subcrassa, setate provecta rubescente. (R.) 



Diam.— Coenobii 0.00124"— 0.0035"; cell, (distantise interlobos) 0.00026"— 0.00069". (R.) 



Syn. — P. Selenasa, Ktz. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 73. 



Sab. — ^Rhode Island, Bailey. 



Cells crescent-shaped, arranged in one or more circles round one or two central ones, connecting 

 medium colored. (A.)'' 



P. pertnsfum, Ktz. 



P. coenobio orbiculari, lacunis pertuso, magnitudine vario, e cellulis plerumque l-|-5-)-10-|-15 

 (in formis quibusdam ad 64) composito ; cellulis periphericis basi tantum laxe connexis, ad 

 medium usque bilobis, lobis rectis, in cornua hyalina modo subacuta modo obtusa vel trun- 

 cata plus minus productis, centralibus plus minus exacte quadrangularibus, et in antica parte 

 et utrinque emaginatis, omnibus laevibus, locellis pallioribus finis instructis. (R.) 



Dmm.— Transv. cell, perfecte evolut. circiter 0.00065"— 0.00089". (R.) 

 Syn. — P. pertusum, Ktz. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 75. 

 Cells arranged in circles round one or two central ones ; inner cells quadrangular, sides concave 

 and leaving angular vacant intervals; the outer cells with square bases, externally triangu- 

 larly notched, the subdivisions tapering to an acute point. L. 1-2266" ; B. 1-3268". (A.) 



P. constrictum, Hassal. 



P. coenobio orbiculari vel suborbiculari, Isete viridi, continuo, Isevi ?, e cellulis 16 (ad 1 -f 5 + 

 10) vel 32 (ad 1 -f 6 -I- 10 -I- 15) formato; cellulis periphericis irregulariter bilobis, sinu 



' The best exposition of this genus is to be found in Braun's Unicellular Algae. 

 ' The letter A used here signifies that the description is copied from Mr. Archer in Prichard's Infu- 

 soria. 



13 June, 1872. 



