52 NATUKAL HISTOKY SOCIETY OF DUBLIN. 



terminal notch, placing it apart from Tetmemorus (Ralfs). I do not 

 believe that it can be mistaken for any other species in the genus Penium, 

 its minute size alone readily distinguishing it. Irrespective of its mi- 

 nuteness, there is no other species of Penium in which the length of the 

 cell is so short in proportion to its width, all other species, with the ex- 

 ception of P. (Dysphinctium) annulatum (Nag.), being several times 

 longer than broad, while the species just referred to is about twice as 

 long as broad. And this relationship of comparative length and breadth 

 I believe to be in this family a by no means unimportant character, 

 though undoubtedly of so little value in others. Nor would I wish to 

 be understood that here even this character is decisive; but when it is 

 found that a pretty constant steadiness of relative length and breadth 

 of most species is associated with other characters, it becomes, I think, 

 a useful and readily applied diagnostic distinction, ancillary but subser- 

 vient to other more special ones. Yrom Penium annulatum (Nag.), then, 

 besides its less comparative length, this species is distinguished by its 

 n on- cylindrical outline and smooth cell-membrane. Prom P. navicula 

 (Breb.) this species is distinguished by its less comparative length, and 

 by its broadly elliptic or barrel-shaped, not navicular, cells, and by the 

 want of a terminal clear space with moving granules. There is no other 

 Penium for which it could possibly be mistaken. 



Prom Cosmarium curtum (Breb.) it is distinguished by its shorter 

 comparative length, and the entire want of a constriction, by its broadly 

 elliptic, not attenuated ovate outline, and by the "fillets" of the endo- 

 chrome being far less decidedly marked. Prom Cosmarium cucurlita 

 (Breb.) it is separated by its much smaller size, by the entire absence 

 of a constriction, by its elliptic form, and by its smooth, not punctate, 

 cell-membrane. 



Prom all these, and every other member of the family, it is, more- 

 over, further distinguished by the remarkable form of its zygospore. It 

 is possible that this may in some measure agree in nature with that of 

 Tetmemorus lavis (Ralfs.) ; but even if found isolated, it could not be 

 mistaken for that of that species, differing, as it does, in form and size 

 therefrom. But, as before stated, this plant is no Tetmemorus, want- 

 ing, as it does, a terminal notch and central constriction. I say it is 

 possible that the quadrate, or cruciately-lobed zygospore of this species, 

 may agree in nature with that of T. laivis- but although there is in all 

 my specimens of the new Penium a tendency in the cell-contents of the 

 zygospore to become collected towards the middle, I have not once no- 

 ticed the formation of an inner coat, as happens in T. Icevis. Yet it may 

 have been that my specimens were not sufficiently matured. We are 

 here, too, reminded of the zygospore in Closterium Cornu and others 

 (Stauroceras, E/utz.); but even if found isolated, the zygospores never 

 could by possibility be mistaken the one for the other. There is the 

 common circumstance, however, that the parent cell-membranes remain 

 persistently attached to the zygospore. Thus this little Penium possibly 

 points out new cross affinities, to Tetmemorus on the one hand (although, 

 as is well known, in that genus two forms of zygospore occur, as indeed 



