FRESH-WATER A L G .E OF THE UNITED STATES. 155 



enoriiiiter lipxagoiiis, angulis in pi'Dcessns rectos ct divcrgcntes productis, dorso proccssibus 

 similibus 4-5 iu.stnicto ; seraicellulis a vertice poI\'gouis vel suljoi'bioularibus margine proces- 

 sibus numerosis, pleruiiique 9 instructo ; dorso pfoce-ssibus 5-8 instnictis; proccssibus omni- 

 bus similibus, granulato-deutatis, apioe acliroo siniplicibus, bifurcatis vol flssis. 



Diam. — A vertice cum processibus, rnVuV = •004'75". Sine process. xs'uVij" = -002". 



Syn. — St. munitum, Wood, Proceed. Ac. Nat, Sc, 1869. 



Bob. — In lacu Saco, Xew Hampshire; (Lewis) Wood. 



S. rather large, about one-half longer than broad, slightly constricted in the middle ; semicells 

 from the front irregularly hexagonal, the angles prolonged in straight divergent processes, 

 and tlie surface furnished with four or five similar ones; semicells from tiic vertex polygonal 

 or suljorljicular, tlie margin furnished with numerous |)rocesses, mostly about nine, and also 

 with 5-S on the dorsum; jirocesses all similar, granulate-dentate, their transparent apices 

 simple, bifurcate or torn. 



I^cmarks. — Tliis species is most closely allied to St. furcigerum, Bivb., from 

 •which it is at once distinguished by the orbicular vertex. The constriction between 

 the semicells is also very different. In St. muuUum it is a gradual, not very deep, 

 hour-glass contraction ; in St. furcigrrum it is very narrow and linear. 



Fig. 13 «, pi. 13, is a front view of this plant magnified 260 diameters; fig. 13 i, 

 the end view of the same. 



St. eiistephaniiin, (Euri:.) Ralfs. 



St. laterum integrornra angulis productis apice spinulosis, spinularum furc.atarum corona media 



dorsali. (R.) Species mihi ignota. 

 Syn. — Deanddium eustei)hanuin. Eiirenberg, Terbreitung and Einfluss der !Mikro.sk. lA'ljens 

 in Slid- und Nord-Amerika, t. 4, f. 23. 

 Slaurastrum eustephanum, (Eiirb.) Ralfs, British Dcsmidica\ p. 215. 

 Steplianoxanlhium eustephanum, KOtzi.n'g. Rabenhorst, Flora Europ. Algarum, Sect. 



III. p. 221. 

 Staurastrum eustephanum, R.\lfs. R.\be.\'iiorst (Joe. cit.) 

 Hah. — West Point, New York ; Bailey. 



End view triangular with six cmarginate spines on the upper surface; each angle terminated 

 by a short ray tipped with spines. (Ralfs) 



St. senariiiin, (Ehrb ) Ralfs. 



Anteeedenti simile sed laterum parietibus spinulis furcatis binis (sex), corona dorsali senaria. 

 (R.) Species milii ignota. 



Syn. — Desmidium senarium, Eiirenberg, Terbreitung. T. IV. 



Steplianoxanlhium senarium, KiJTZiNU. Rabenhorst, Flora Europ. Algarum, Sect. III. 



p. 220. 

 Staurasinim senarium, (Eiirb.) Rai.fs, British Desmidicffi. Rabenhorst, (loc. ci/.) 



Segments smooth in end view with three angles, each terminating in a short process tipped by 

 minute spines, without lateral processes, but with six others confluent at their bases ou the 

 upper surface, divergent and forked. (Archer.) 



Genus XANTIIIDIUM, Ehrb. 



Cellulse singulfB vel gemina? concatenate, infiato-rotundatw, profunde constrictae ; semicelluliE 

 compressas, oblongas, hcmisphsericae vel subquadrangulares, centre in tubcrculum rotundatum vel 

 truncatum et deuticulatum protuberantes, ex transverse oblongo-rotundata;. Cytiodornia firinum 

 setis, aculeis vel spinis simplicibus aut bi- tri-furcato-divisis armatum. Massa chlorophyllacea 

 radiatim expansa, Zygospora^ arniade. (11.) 



