FRESH-WATER ALGiE OF THE UNITED STATES. 89 



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

 angles, sometimes radiately elongate, either entire or bifid; mostly armed, oblong-elliptical when 

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

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



Propagation unknown. 



Bemarks.-^This genus was described by Nsegeli in his "Gattungen Einzelliger 

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

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



P. enorme, (Ealfs) De Baky. 



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

 mucronatis. (R.) 



ZJiam.— 0.0011"— 0.0016". (R.) 



Syn. — P. enorme, (Ralfs) De Bart. Rabenhoest, Flora Europ. AlgaruBa, Sect. III. p. 62. 

 Staurasfrum enorme, Rales, British Desmidiese. 



Hab. — Florida. Bailey. 



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

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

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

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

 difference 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 emarginate, and frequently 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 apex." — Balfs' British 

 Desmidiese, p. 141. 



Genus SCENEDESMUS, Meten. 



Cellulse polymorphse, utroque polo aequales vel insequales, ssepe in cornu spiniforme productae, in 

 setate perfecto 2-16 aut in seriem simplicem aut parenchymatice arete conjunctae et coenobium con- 

 stituentes ; cytioplasmate initio homogeneo, postea granuloso, vesicula chlorophyllosa centrali vel 

 sublaterali et ssepe locello achroo laterali instructo. 



Propagatio fit cytioplasmatis divisione succedanea, unde gonidia oriuntur, quae intra cellulam 

 matricalem jam in coenobium planum sese cpnjungunt et membranas 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 coenobium. Cytioplasm in the beginning homogeneous, afterwards granular, furnished with 

 a central or sublateral 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. 



jRemarfe,— According to linger, in the genus Soened6smm the cells never exist 

 singly, but always in families. 



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

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



12 May, 1873. 



