90 FRESH-WATER ALGiE OP THE UNITED STATES. 



or families. The latter were exactly like those of the European forms, at least 

 in one of the two species, and I do not therefore think it justifiable to indicate a 

 new genus. Moreover, I have certainly seen single cells, belonging to a species 

 which agrees precisely in its characters with a European form, save only in the 

 occasional existence of these single cells. 



I have never studied the method of propagation, but it is said to occur by the 

 division of the cytioplasm of a large cell into a minute coenobium composed of 

 two or more cells, which remains for some time within the walls of the mother- 

 cell, but is finally set free by the solution of the latter. 



The cells are mostly much longer than broad, cylindrical, elliptical, or oval, but 

 in one species herein described they are habitually globular. 



a. Cellulae inermes. 



a. Cells unarmed. 



S. obtusnsi, Meten. 



S. cellulis oblongis rel ovatis, utroque polo obtusis, 4-6-8 modo arete modo laxe in seriem 

 simplicem aut rectam aut dupllcem obliquam conjunctis, diametro 3-5 plo longioribus. (R.) 



Biam.—TTa.nsY. max. 0.00023"— 0.00028". (R.) 



Syn. — S. obtusus, Meten. Rabenhokst, Flora Europ., Algarum, Sect. III. p. 63. 



Sdb. — Georgia : Rhode Island, Bailey. 



Cells oblong or ovate, obtuse at each end, 4-6-8, partly closely partly laxly conjoined into a 

 simple series either straight or oblique and double, 3-5 times longer than broad. 



Eemarh. — I have never met with this species. 



S. acntus, Meten. 



5. cellulis fusiformibus, vel ovato-fusiformibus vel ovatis, utrinque acutis sed inermibus, inter- 

 dum singulis sed plerumque in seriem aut simplicem rectam aut duplicem inordinate alter- 

 nantem dispositis, arete concretis, diametro 2-4 (6?) -plo longioribus. 



i>8am.— Trans, vag. max. ? .00016". 



Syn. — S. acutus, Meten. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 64. 



Hab. — Prope Philadelphia, Wood. Rhode Island, Bailey. 



Cells fusiform, or ovate-fusiform or ovate, acute at each end but unarmed ; sometimes single 

 but mostly conjoined into a single straight series or into an irregularly alternate double series 

 2-4 times longer than broad. 



RemarJcs. — This species is common around Philadelphia. Our specimens agree 

 very well with the descriptions and figures of the European, excepting that occa- 

 sionally a cell is single, and that none which I have measured have attained the 

 size given by Prof. Rabenhorst as the maximum, namely, 0.00023". According 

 to Rabenhorst, S. ohliquus, Ktz., is only a variety of S. acutus, Meyen. It has 

 been found by Prof. Bailey in South Carolina, Georgia, and Rhode Island. 



6. Cellulae armatee. 



b. Cells armed. 



