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 striae 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.) 



Cytheropsis (M'Coy). 

 Syn. Cytherina (Burm., not of Lamarck). 



I provisionally propose this name for the little bean-shaped 

 bivalve Entomostraca of the palaeozoic 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 clearly more logical to refer those 

 fossils to the former group, which we believe to have abounded 

 at the palaeozoic 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 Maastricht 

 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 

 palaeozoic 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. 



