ZOOLOGICAL AND BOTANICAL ASSOCIATION. 1 1 % 



meters of Docidium, and which are very manifest in all the British 

 species, as well as in the American, as figured in Ralfe. This, I admit, 

 however, must bo stated with one slight exception, for here I am not 

 unmindful of Docidium minutum (lial/s). In that species there appears 

 a distinct central constriction, but there is no evident inflation at the base 

 of the segments. There appears a terminal, well-defined cavity in which 

 are moving granules, not as in the first of the new forms which I now 

 bring to notice, a space, left merely by the withdrawal of the endochrome, 

 in which these move. Moroovor, Docidium minutum is not a filamentous 

 form. Mr. llalfs himself allows Docidium mperum (Brib.) to remain 

 in that genus unwillingly, and merely because he had no better course 

 open. But perhaps it might possibly by some be urged that the es- 

 sential characters of the genus Docidium might with propriety be altered 

 by omitting those before mentioned, which seem to be abundantly suf- 

 ficient to exclude the three forms in question ; or some might say they 

 might be kept in Docidium as aberrant members of the genus. It occurs 

 to me that the answer to such suggestion is found in the fact of these 

 three forms being filamentous ; else we might with as great propriety 

 and as good reason include, for instance, Sphserozosma with Cosmarium, 

 or Desmidium with Staurastrum, the separated joints of which filamen- 

 tous genera resemble the free genera Cosmarium and Staurastrum re- 

 spectively, more than do the separated joints of the filamentous forms 

 under consideration resemble the apparently natural genus Docidium, as 

 at present constituted. The same considerations will, I think, distin- 

 guish any of these forms from Penium. There is, perhaps, some resem- 

 blance, in a separated joint, to such forms as Penium truncation or 

 Penium cylindrufi, but the ends in both these species are rather rotundato- 

 truncate than truncate, while it seems that the affinities of Penium are 

 rather with the Palmellaceous Algaj, through such species as Penium 

 Brdbisionii, whereas I apprehend the forms now described approach the 

 Zygnemaceous Algte. 



These are, then, I believe, filamentous Desmidiaoeae, the individual 

 joints of which bear some resemblance to Docidium (still less to Penium 

 and Closterium), while the filament does not resemble any other estab- 

 lished filamentous genus. I believe, then, the first described form must 

 be taken as the type of a new genus, and which, so far as I know, will 

 be the only example of a fixed or attached Desmid ; along with which 

 I would venture to associate Docidium asperum (Brtb.), and, as a matter 



ZOOL. A BOT. PROC. SOC. TOL. I. Q 



