FRESn-WATER A L .E OF THE UMTED STATES. 91 



S. poIyiuorphii<$, Wood. 



S. cellulis fusifurmibus, aut ovalibus aut ellipticis aut globosis, singulis aut 2-8 conjunctis, 

 plerunique utroque polo aculeo unico, iiiterdum aculcis duobu.Si, instructis: apicibus obtusis, 

 acutis, vel acutissimis ; aculeis gracilliinis, rectis, modice clougatis, inclinatis. 



Dza?n.— 55V'— TfiW ; plerumque 3-0V5". 



Syn. — S. polymotyhuit. Wood, Prodromus, Proc. Am. Philos. See, 1869, p. 135. 



Hab. — In aquis quietis prope Caiudeu, New Jersey. 



S. cells fusiform, or oval, or elliptic, or globose, single or 2-7 conjoined, furnished in most 

 cases with a single spiue, sometimes 2, at each end ; ends obtu,se, acute, or very acute; spines 

 exceedingly slender aud acute, straight, moderately lung, inclined. 



Remarks. — This plant was found in a quiet pool, filling the water in such num- 

 bers as to make it opaque and very green. The color of the cells, as first obtained, 

 under the microscope, was a vivid green, biit, the water containing them having 

 been placed in a dish, during the slow desiccation which followed the color of tiie 

 cells changed to a golden yellow. 



Fig. 1, pi. 11, represents different forms of this species magnified 450 diameters. 



S. qiiadi'icauda, (Tlrpin) Breb. 



S. cellulis oblongo-cylindricis, utroque polo obtuse rotundatis, 2-4-8 aretissime conjunctis, 

 ordine aut simplici recto aut duplice alternante, omnibus rectis, medianis inermibus vel his 

 illisve apice uno altcrove aculeo curvato instructis, extimis utroque apice sapius item dorso 

 armatis. 



Z)iaw?._0.00035"— 0.00039"; long. 0.00091". 



Syn. — S. quadricauda, (Ttjrpin) Breb. Rabenhorst, Flora Europ. Algar., Sect. III. p. 65. 



Hab. — Rhode Island, Bailey. Pennsylvania, Wood. 



Cells oblong-cylindrical, obtusely rounded at each end, 2-4-8 very closely conjoined either in a 

 single straight series or a double alternating one, all straight, the median unarmed or some of 

 them with the apex furnished with a curved spine, the external with both apices and some- 

 times the dorsum thus armed. 



Remark. — Fig. 2, pi. 11, represents this species magnified 750 diameters. 



S. rotiindatus, Wood, (sp. nov.) 



S. cellulis globosis vel subglobosis, spinulis longissimis, rectis, gracillimis, acutissimis, 3-6 

 armatis, aut singulis aut geminis aut 3-4 arete duplice conjunctis. 



Diam..—^^\-s" to ^^Vtt"- 



Hab. — In aquis quietis prope Philadelphia. (Dr. Chapman.) 



Cells globose or subglobose, armed with three to five very long, slender, acute, straight spines, 

 single or in pairs, or three to four closely conjoined in a twofold rank. 



Remarks. — The cells of this species are globular, and, when more than two, 

 they are arranged in two rows placed at right angles one to the other. The con- 

 tents of the cells are markedly granular, and the endochrome a bluish-green, and 

 from the surface of the walls project outwards, very long and fine, rigid hair-like 

 spines. 



It seems scarcely correct to place this plant in the genus Scenesdesmus, but I do 



