OSTRACODA. 685 
Oytherella? subrotunda.] 
these appear to be within the limits of the genus. Prof. Jones has also referred 
several Lower and Upper Silurian species to the genus, but here, it seems to me, the 
oeneric relations are in every case at least doubtful. The following two species at 
any rate, are almost certainly not Cytherella, yet they must be placed here because 
their known characters are more in accordance with this genus than with any of 
the others that have been established. 
At present the principal diagnostic feature of Cytherella, that is, with the 
paleontologist, is the rabbeted edge of the right valve. This peculiarity, if my 
memory is not at fault, has not yet been shown to exist in any of the Silurian 
species hitherto referred to the genus. It does however exist, and very strougly 
developed too, in an undescribed species from the lower beds of the Cincinnati group. 
In this species, however, unless all the specimens seen (about twenty) are of one 
valve only, the edges of doth valves are about equally grooved. 
For remarks on Cytherellina, Jones and Holl, see under Bythocypris and B. 
cylindrica. 
CYTHERELLA ? SUBROTUNDA, 2. Sp. 
PLATE XLIV, FIG, 43. 
Sizz.—Length 0.5 mm.; hight 0.45 mm. 
This species is founded upon a single carapace attached to the surface of a 
fragment of the zoarium of Pachydictya foliata. The smaller valve is exposed to 
view, and around it the overlapping edge of the larger, presumably the right valve, 
is distinctly defined. The outline is broad-oval, almost circular, and as near as can 
be determined, the surface of the smaller valve is moderately and quite uniformly 
convex, and exhibits neither a central depression, a tubercle, nor markings of any 
kind. The specimen was found in association with valves described on a preceding 
page as Schmidtella? subrotunda. They are distinguished by a small, subcentral 
tubercle, but as they have the same rounded outline, it is possible that a better 
preserved series of specimens may show them all to belong to one species. That the 
synonomy may, in case the possibility is converted into a fact, be simplified, I have 
used the same specific name for both. 
Formation and locality—Lower third of the Trenton shales, Minneapolis, Minnesota. 
