414 On the Classification of some British Fossil Crustacea. 
about twice and a half longer than wide, greatest width of the 
side and curvature of the margin about one-third from the 
anterior end, which is elliptically pointed ; posterior end ob- 
tusely rounded, the oblique truncation nearly effaced ; ventral 
margin convex; ocular spot elevated like a small tubercle, 
twice its diameter from the dorsal line, and about one-fourth 
the length from the anterior end; I believe the striz of the 
surface have the direction usual in the genus, but they are 
very delicate. Length 1 inch 3 lines, greatest width of the 
sides 6 lines. 
The elliptical form, prominence of the eye-spot, and its distance 
from the anterior end, mark the species well. 
Rare in the Upper Ludlow rock of Benson Knot. 
(Col. University of Cambridge.) 
‘ytheropsis (M‘Coy). 
Syn. Cytherina (Burm., not of Lamarck). 
I provisionally propose this name for the little bean-shaped 
bivalve Entomostraca of the paleozoic rocks, which were formerly 
referred by myself and others to Cythere, but which Dr. Bur- 
meister suggests should rather be referred to the Phyllopoda. 
As apparently the same forms of carapace exist both in the Phyl- 
lopoda and Lophyropoda, it is cleatly more logical to refer those 
fossils to the former group, which we believe to have abounded 
at the paleozoic period, than, by placing them with the analogous 
types of the Lophyropoda, to quote the occurrence of that tribe 
at those early periods without sufficient reason. 
In M. Bosquet’s memoir on the Entomostraca of the Maéstricht 
Chalk, he proposes to refer all the ornamented species which I 
have described and figured in my Synopsis of the Mountain 
Limestone Fossils of Ireland, to the recent genus Cypridina ; this 
I suppose is on the supposition that the tubercles represent the 
lateral eyes of that genus; but though the eyes were possibly 
lateral also in the fossil group, there is no evidence of the fact, 
nor reason for supposing they were not similarly placed in the 
plain ones ; I therefore think the plain and ornamented species 
should not be divided, and for the above reason think they are 
both better placed with the Phyllopodes. It is singular that 
Prof. Burmeister, in establishing this genus and stating that the 
palzozoic limestones contained the only representatives of it, 
should have applied to them the Lamarckian name Cytherina, 
which is a mere double emploi of Latreille’s recent genus Cythere. 
The carboniferous genus Bairdia (M‘Coy) is distinguished from 
the above by its attenuated recurved extremities. 
