FRESH- WATER ALGJ^; OF THE UNITED STATES. 89 



Cells single, segregate, swimming free, compressed, 3-4— 8-anglecl, more or less produced as to their 

 angles, sometimes radiately elongate, either entire or bifid; mostly armed, oljlong-ellii)tical when 

 viewed laterally, at each end rounded or subtrnncate. Cytioderm thin, smooth ; chloropiiyi mostly 

 granular, equally distributed through the cell, sometimes mixed with reddish oil-drops. 



Propagation unknown. 



Remarks. — This genus was described by Naegeli in his " Gattungen EinzeUiger 

 Algen," and, although I have never seen any specimen of it, it chiiins a place here, 

 because one species has been found in this country by Prof. Bailey. 



P. enorme, (Ralfs) De B.\ky. 



P. tetraediicum, angulis productis achrois profunde bilobis, nonnunquam repetito-bilobis, lobis 

 mucronatis. (R.) 



X>mm._0.0011"— 0.0016". (R.) 



Syn. — P. enorme, (Ralfs) De Bary. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 62. 

 Slaurastruvi enorme, Ralfs, British DesmidieiB. 



Eah. — Florida. Bailey. 



"Frond irregular or quadrate, spinous; end view three or four-lobed ; lobes broad, more or 

 less emargiuate or bifid, and terminated by spines, which are either simple or branched. 

 Sometimes the front view differs but little from the end one, usually, however, there is a 

 slight constriction or sinus at the junction of the segments, but I have never observed any 

 diifcrence in the endochrome at that part. The spines, which are almost confined to the 

 angles, are irregular, some simple and some branched. The end view has three or four broad 

 and very irregular lobes ; these are spinous and more or less emargiuate, and frequeutly one 

 lobe is much broader and more spinous than the others. The spines on such lobe form two 

 groups, separated by the notch; they vary much in size and are either simple and subulate, 

 or else forked; sometimes the forked spines are again divided at the apes." — Malfs' British 

 Desmidieae, p. 141. 



Genus SCENEDESMUS, Meten. 



Cellule polymorphaj, utroque polo jpquales vel intequales, seepe in cornu spiniforme productse,' in 

 ffitate perfecto 2-16 aut in seriem simplicem aut parenchymatice arete coiijuncta3 et coenobium cou- 

 stituentes ; cytioplasniate initio homogeneo, postea grauuloso, vesicula cliloropliyllosa centrali vel 

 sublaterali et siepe loccllo achroo laterali instructo. 



Propagatio fit eytioplasmatis divisione succedanea, unde gonidia oriuntur, qua; intra eelhiliiin 

 matricalem jam iu ccenobium planum sese conjungunt et membran;e matricalis ruptura vel dissolu- 

 tione prodeunt. 



Cells polymorphous, equal or unequal at the ends, often produced into a spine-like horn, in the 

 perfect state 2-16 closely conjoined, either as a simple series or in a parenchyma-like manner so as to 

 form, a ccenobium. Cytioplasm in the beginning homogeneous, afterwards granular, furnished with 

 a central or sulilateral chlorophyllous vesicle, and often with a lateral transparent spot. 



Propagation occurring as a succedaneum to the division in the cells, whence arise gonidia, which, 

 already within the mother-cell, join themselves into a coenobium, and are finally set free by the rupture 

 and dissolution of the maternal cell-wall. 



Remarlis. — According to Unger, in the genus Scenedesmus the cells never exist 

 singly, but always in families. 



Two of the species here described as representatives of tlie genus certainly do 

 not conform to this, for I have frequently seen them both separate and in coenobia 



12 May, 1S73. 



