120 BRITISH DESMIDIACE^E. 



ship with each other, in which the parietal disposition of 

 chloroplasts had been independently acquired. Moreover,, 

 this so-called parietal disposition of chloroplasts is a matter 

 for further investigation. In most cases careful examination 

 shows them nor/ to be truly parietal, but of an irregular 

 character, and they may be axile in one semicell and parietal,, 

 or partially so, in the other. One of the principal species 

 included by Lundell in his subgenus Pleurenterium was St. 

 grande Bulnh., but the careful investigations of Liitkemuller 

 show that in most individuals of this species the chloroplasts 

 are axile. Also in St. Brasiliensc var. Lundellii, another 

 Desmid placed by Lundell in Pleurenterium, the chloroplasts 

 are invariably axile. 



As mentioned above, there is one feature possessed by a 

 considerable percentage of the species of Staurastrum which 

 does not occur in any other genus of Desmids,"* namely, the 

 production of the angles of the semicells into hollow pro- 

 cesses. We have, therefore, regarded this character as of 



' ' O 



fundamental importance, and used it as a basis for the 

 primary division of the genus into tw^o large groups of 

 species. In each division we have arranged the species under 

 several fairly well-defined sections. 



The outline of the scheme is as follows : 



Division I. Angles of semicells not produced into processes. 



a. Cells with only a slight constriction and a very small sinus, 



* t/ 



semicells subcylindrical in the basal part and angular at the apex. 



SECTION A. Cells subcylindrical, granulate or verrucose. 



4 species. 



SECTION B. Cells subcylindrical, smooth. 



1 species. 



b. Cells with a well-marked constriction and a deep sinus, semi- 

 cells 3-6-angled, or rarely compressed. 



SECTION C. Cells smooth or punctate, without spines, verrucse,. 

 or granules. 



21 s 



SECTION D. Cells furnished with small granules, regularly or 

 irregularly disposed, often covering the whole cell-wall or sometimes 

 more or less restricted to the angles. 



15 species. 



* The only other known processes of this natxire are those on the lobes of 

 a few species of Micrast&rias, such as M. americana, M. Mahabuleshwarensis, 

 M. anomala, M. muricata, M. Nordstedtiana, etc., and those at the apices of 

 the elongated semicells of Triploceras. 



