Desmidiece.'] ixfusobial animalcules. 289 



yet a definite number of corpuscles cells, forming a memhranoiis poly- 

 pary (compound frond.) The frond is flat, stellate, multi-locvilar, and 

 reticulate ; and each of its corpuscles has its margin extended into a 

 tubular and pcr^'ious horn. Asterodidyon has a general resemblance 

 to Monactinus and Pediastrum. 



AsTEEODicTTON- frianguhtm. — The smooth ti'iangular corpuscles are 

 combined in triple series, and fomi a stellate disc. This compound 

 star has its centi-e void, with an innermost row of five, a middle of 

 ten, and a marginal of fifteen to sixteen cells. Diameter of each 

 frustule l-1080th. ; of the entii-e star l-216th. JS'ear Berlin. 



A. ovatum. — Corpuscles granular, ovate, terminated by a long 

 style, and ari'anged in two concentric circles, forming a star : three 

 cells form the inner row, and ten the outer. Diameter of each 

 l-780th., of the entire star 1 -312th. ; near Berlin. These forms, when 

 sometimes irregular by monstrosity, very closely resemble the Monac- 

 tinus simplex and M. acutangulus, of Corda. 



Genus Moj^Acri]ST:s. — Compound ; corpuscles numerous, connected 

 so as to form a membranous polypary (frond) flat, stellate, multilo- 

 cular, not reticulate, and having its cells in a single circle. Each 

 cell tenninated by a solitary style (with a single aperture.) 



Pediastrum, which most nearly resembles it, differs in its forked 

 or bidentate cells (and in its double aperture.) Ehi-enberg believing 

 in the animal nature of the Desmidiece, the apertiu'es are important 

 to his view. 



M. simplex (Corda.) 



MoxACTrNTJs acutangulus (Corda.) 



Genus ScEiTEDESjnjs (Ralfs.) — Frond composed of two to ten frisi- 

 form or oblong cells, an'anged side by side in a single row, but after 

 division in two alternating rows ; division obKque. Cells entire ; 

 in some species the outer ones are lunate. There is no constriction or 

 sutxu'e at the middle, and the endochrome is not divided into two 

 portions by a transverse band. The division of the cells is oblique, 

 and not ti'ansverse, as in most genera of the Desmidiece and as they 

 all divide simultaneously, two rows are produced, which are held in 

 opposition some time after division is complete, by the connecting 

 hyaline matrix. 



The endochrome is, in general, very pale, and the starch granules 



