Dr. G. C. Wallich on Desmidiacea from Lower Bengal. 187 



1. Hyalotheca, Ehr. 



Filament cylindrical. Joints having either a slight central 

 constriction or a double rim at one or both extremities. End 

 view circular. 



1. H. dissiliem, Ralfs. Filament very slightly constricted at the 

 centre of each joint. 



Frequent. Length of joint from -0003" to -0008"; breadth 

 of joint -0003" to -0012". 



2. H. mucosa, var. /3. Joints not constricted, but having a 

 double rim at both their extremities. 



Length -0007"; breadth -0004". 



This variety differs from the form described and figured by 

 Mr. Ralfs (' The British Desmidiese/ p. 53, tab. 1) in having the 

 double rim at each extremity of the joints, instead of only at one 

 of these. Moreover, these rims, on careful illumination, are 

 found to consist of rows of minute elevated puncta. 



Both H. dissiliens and the last-named variety of H. mucosa 

 occur abundantly, intermixed with the larger Algse and with 

 Anacharis alsmastrum'^, during the height of the rainy season, 

 in the turbid and swollen water-courses. In this respect they 

 differ from the great mass of the Desmidiacese. 



2. Desmidium, Ag. 



Filament compressed, triangular, or quadrangular. Joints 

 constricted deeply. United by minute, projecting, mucous 

 cushions, which spring from the outer portion of each lobe or 

 extremity. 



It will be observed that the above definition is framed with a 

 view to include the plane and triangular varieties of Aptogonum 

 Desmidium, which differs in no material point from the genus 

 now under notice, as will presently be seen. But whilst I concur 

 with Brebisson, Meneghini, and Kiitzing in uniting the species 

 referred to under Desmidium, I would submit that the pecu- 

 liarly marked character exhibited by Aptogonum Baileyi and a 

 new variety obtained from Lower Bengal — namely, the entire 

 absence of constriction on the joints, which accordingly are not 

 divided into segments — is of sufficient importance to demand 

 their separation. 



* It is worthy of notice that this curious plant, which is generally 

 understood to have been introduced into Britain from North America, may 

 with equal probability have been introduced from Bengal along with the 

 "Jute" fibre (Corchorus capsularis, a staple article of export to this 

 country), which is subjected dm-ing preparation to long-continued macera- 

 tioa ia the streams and pools. 



13* 



