232 NATURAL HISTORY SOCIETY OF DUBLIN. 
Although?the Rhizopoda are a group of which the sea harbours the 
greatest variety, as well as the most beautiful forms, yet are those 
which find a habitation in the fresh waters far from being without 
their interest—nay, few other animal groups have of late awakened 
more lively attention. Therefore, such a communication as the present 
—even though it but humbly essays to bring to notice some types 
which seem rarely or not before to have met observation in the fresh- 
water, without being able to add to our knowledge in a physiological 
point of view as regards these lowly beings—may not, perhaps, be 
wholly destitute of value or interest. 
Such, indeed, is the frequency with which certain freshwater forms 
are met with, that no observer with the microscope can fail to be more 
or less familiar with the commoner species; again and again they pre- 
sent themselves, and, to my eyes at least, they seem again and again 
ever recognisable; and this strikes me, indeed, so forcibly that I, for 
my part, cannot at all coincide with those who hold the view that 
there is no fixity or definiteness amongst these beings, and that all the 
varied forms—some more, some less abundant—which present them- 
selves, are but simply phases of one and the same protean Rhizopod. 
Such being the views which an at first casual, and afterwards more 
special, examination of these beings had impressed upon me, I natu- 
rally began to think it probable that the types of Rhizopods of the 
fresh waters might not be altogether confined to the ordinary ones 
already recorded in books, represented by the genera Difflugia and Ar- 
cella, Kuglypha, Cyphoderia and Trinema, Gromia, &c.; and though 
evidently the fresh waters are by no means so rich in types or in indi- 
vidual forms as the sea, still my look out for novelties was not altoge- 
ther unrewarded. 
The state of knowledge of the structural and developmental affini- 
ties of the known types is as yet so imperfect, that existent arrange- 
ments of this group to be found in books are still unsatisfactory. This 
circumstance renders it a matter of difficulty in bringing forward the 
following new or little-known forms, to determine exactly with which 
to begin, although these, indeed, may hardly exceed a dozen. Still 
they demand several new genera for their reception. The comparative 
fewness of generic types in the fresh waters renders the intervals 
between them seemingly wider than if the species were a8 numerous as 
those of certain marine groups. The sequence in which I shall put 
them before those who take an interest in such forms is, therefore, a 
matter of the less importance. I shall then commence with two forms 
which come the closest to the marine ‘‘ Radiolaria’’ of Haeckel, by rea- 
son of possessing solid parts or skeleton* (for none of them actually 
belong to that extensive group, so lavishly rich in marvellously beau- 
tiful forms, by reason of the absence of the seemingly all-important 
part of the organization—the ‘‘ central capsule’), and then I shall pass 
on to other ‘‘shell-less’’ forms more approximating to the ordinary Ac- 
* Haeckel, ‘‘ Die Radiolarien (Rhizopoda radiaria”), pp. 25, 69, 243. 
