34 Mr. HassalPs Notices of British Freshwater Conferva. 



Dimensions. inches, lines. 



Diameter of orbit 1 2 



Length of ventral fins 4 6 



pectorals 3 



caudal 3 



Height of anal 3 3 



dorsal, measured directly 2 7 



dorsal, measured along the rays 4 6 



body between fore-part of dorsal and anus 10 2 



fish including anal and dorsal 14 2 



[To be continued.] 



IX. — Observations on the genera Zygnema, Tyndaridea, and 

 Mougeotia, with descriptions of new Species. By Arthur 

 Hill, Hassall, Esq., M.R.C.S.L., Corresponding Mem- 

 ber of the Dublin Natural History Society. 



It is the general belief of Cryptogamic physiologists that 

 union of the filaments of the different species composing the 

 genera Zygnema, Tyndaridea, and Mougeotia is indispensable 

 to the production of fertile spores. This belief I consider to be 

 erroneous so far as the genus Zygnema is concerned, as I think 

 that I have the means of satisfactorily proving. In three spe- 

 cies of Zygnema which I have recently met with, and which I 

 have named Zygnema quadratum, Z. intermedium and Z. angu- 

 latum, the filaments do not unite, and yet all equally produce 

 spores, only two of which, however, it is remarkable to ob- 

 serve, are placed in contiguous cells, and on one side of 

 each of these a cell void of contents is invariably situated, a 

 channel of communication being set up between every two 

 cells, that is, between an empty one, and that which contains 

 a seed, by means of a hollow process, situated at the point of 

 junction of the cells, through which the contents of one cell 

 passes into and mingles with those of the other *. 



From a consideration of the structure of these species, the 

 accuracy of which cannot be doubted, it is evident that con- 

 jugation is not essential to the production of spores, and there- 

 fore, that the supposition entertained by some that the entire 

 of one filament contains fertilizing matter, and the other that 

 which is to be fertilized, is erroneous ; while it is apparent from 

 the disposition of the spores, not more than two being juxta- 

 posed, and of empty cells, that each filament includes both 

 forms of reproductive matter so disposed as to lie in adjacent 

 cells. 



Should future observation disclose the fact, that this alter- 



* A species of Mougeotia. M. notabilis likewise produces spores without 

 conjugation of the filaments. — A. H. H. 



