40 THE ENTOMOSTRACA OF 



more obscure tubercles near the centre, and with one, and sometimes two slight semi- 

 lunar ridges near the dorsal margin ; ventral ridge strongly produced, narrow, and 

 smooth. 



Dorsal aspect sagittate ; end-view triangular. 



Cythere {Cythereis) cormda has many near allies. M. Bosquet has separated (under 

 the name of C. calcarata) the form figured by Reuss (' Haid. Abh.,' iii, t. 10, fig. 18) as 

 C. cornuta [and subsequently referred by him — fig. 18$ to C. ceratoptera, Bosquet, and 

 fig. 18 a to C. coronata, Roemer], because it is spiny on the dorsal and ventral borders, 

 though Roemer's figure of C cornuta appears to indicate a tendency to spinosity on 

 the ventral ridges. C. ceratoptera is of the same typical form, but presenting spines or 

 serrations at every margin. Nor is there much to distinguish C. serrulata, Bosquet, 

 from C. cornuta; and the cretaceous form from the English Chalk which I referred to 

 Bosquet's C. alata has, I believe, no distinction from the C. cornuta of Coiwell and 

 Bracklesham (pi. 4, fig. 19, and pi. 5, fig. 15), except in its somewhat greater 

 squareness and convexity, and the possession of a few more spines. 



The specimens of C. cornuta here figured and described are from the Tertiary 

 sands of Coiwell Bay, Isle of Wight, and from the Tertiary blue clay of Bracklesham 

 Bay, Hampshire. 



No. 6. Cythereis, sp. indeterm. Plate VI, fig. 17. 



Lower Eocene : Thanet Sands, Kent. 



This fragment from the antero-dorsal angle of the left valve of a Cythereis, indicating 

 a ridged valve, possibly resembling C. quadrilatera of the Chalk, occurred in some of 

 the Thanet Sand from Pegwell Bay, near Ramsgate. 



As, from the nature of the deposit, calcareous organisms of any kind are rare, 1 and 

 as this is the only indication of an Entomostracon met with, though I have examined 

 several specimens of the Thanet Sands from Mr. Prestwich's cabinet, I have figured 

 the fragment in this place, as at least an interesting, if not an instructive specimen. 



Sub-genus — Cytheridea, Bosquet, 2 genus. Cytherince et Cytheres, Auctorum. 



Animal a Cythere. Carapace somewhat triangular, or triangularly ovate, the widest 

 part (vertically) being at the anterior third, beneath the anterior hinge ; surface usually 

 pitted, occasionally reticulated : hinge-margin of one valve (right) marked by a series 



1 'Quart. Journ. Geol. Soc.,' vol. viii, p. 245. 2 ' Descript. Entom. foss. Terr. Tert.,' p. 37. 



