FRESH-WATER ALG^ OF 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 unicelkxlar 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 ui the water-nets. 

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



P. Boryauiiiu, (Turpin) Mengh. 



P. coenobio orbicular!, oblongo vel elliptico, magnitudine vario, continue, laste viridi, c cellulis 

 4-8-16-32-64 (rarissinie 128) composite (cellulanim strato simplici, nonnunquam uicdio 

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

 cornibus achrois hyalinis, abbreviatis vel elongatis, teretibus, obtusis vel subobtusis, intenlum 

 capitellato-incrassatis, centralibus arctissime coucretis, polygonis (4-6 angularibus), in autica 

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

 brana decussatim punctata. (R.) 



Z>m??i.— Transv. cell 0.000T95" ; rarius 0.0008S"— 0.00094". (R.) 



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



p. 74. 

 Hah. — 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 tvro long subulate points, the notch narrow. 

 L. 1-2083" to 1-1C33"; B. 1-2733" to 1-2222". (Archer.) 



P. Selejiaea, Kxz. 



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

 cellulis periphericis 'angustis, lunatis, acute lobatis, disci cellulis leviter excisis, central! unica 

 5-angulari, omnium membrana firma, subcra.ssa, aetate provecta rubescente. (R.) 



Diam.—Ccenobii 0.00124"— 0.003.5"; cell, (distantia; interlobos) 0.00026"— 0.00069". (R.) 

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

 Eab. — Rhode Island, Bailey. 



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

 medium colored. (A.)' 



P. pertiisiiin, Ktz. 



P. coenobio orbicular!, lacunis pertuso, magnitudine vario, e cellulis pleruraque l-f5-t- 10-fl5 

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

 medium usque bilobis, lobis rectis, in cornua hyalina mode subaeuta mode obtusa vel trun- 

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

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



Di'am. —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. constrictiiin, Hassal. 



P. coenobio orljicular! vel suborbiculari, laete viridi, continue, laevi ?, e cellulis 16 (ad 1 -f 5 -f- 

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



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

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

 soria. 



13 June, 1872. 



