28 Mr. T. R. Jones on some fossil Entomostraca. 



1 . ? Cythere trigonalis, nobis. Length -^j inch. Pi. III. fig. 5 a, h, c. 



Carapace-valve triangular, convex, finely punctated ; extremities 

 obliquely rounded ; the anterior much broader than the posterior 

 extremity; ventral border nearly straight ; dorsal border angular. 

 Hinge-margin oblique and slightly developed. Right valve nar- 

 rower than the left. Dorsal aspect acute-oval. 



A unique specimen of this interesting form occurs at Clacton, 

 and is identical with an undescribed recent species from Pegwell 

 Bay, except that the latter has teeth or blunt spines on the an- 

 terior and posterior margins, as is usual with the genus Cythere. 



A smooth form, var. la:vis, which occvirs plentifully at Grays, 

 difi'ers from the Clacton specimen merely in the want of pittings. 



Cythere trigonalis approaches distantly in form some old spe- 

 cimens of Ctjpris tristriata, and it more nearly resembles Cythere 

 Hilseana of the cretaceous formation, but differs materially from- 

 both in the structure of its hinge. 



P.S. In a paper lately read before the Geological Society, Mr. 

 W. J. Hamilton notices the occurrence of an extensive deposit of 

 freshwater marl in the Cambridgeshire Fens, in which, in com- 

 pany with still existing land and freshwater mollusks, the follow- 

 ing Entomostraca occur : 



Cypris minuta, Baird.* Caiidona lucens, Baird. 



setigera, nobis. ■ reptans, Baird. 



gibba, Ramdohr. 



EXPLANATION OF PLATE IIL 



Fig. \. Cypris Browniana -{■ 16: a, left valve; b, right valve; c, dorsal 

 profile of both valves ; d, anterior profile of both valves. 



Fig. 2. Cypris tumida + 16 : a, left valve ; b, dorsal profile of both valves ; 

 c, anterior profile of both valves. 



Fig. 3. Cypris setigera + 16 : a, right valve; h, dorsal profile of both 

 valves; c, anterior profile of both valves. 



Fig. 4. Cypris gibba -i- 16 : a, left valve ; b, dorsal profile of both valves ; 

 c, anterior profile of both valves. 



Fig. 5. Cythere trigonalis + 8 : a, left valve ; b, dorsal profile of both 

 valves ; c, antei'ior profile of both valves. 



Fig. 6. Candona torosa -\- 16 : a, left valve, young; b, left valve, adult; 

 c, right valve, adult ; d, dorsal profile of both valves, adult ; e, an- 

 terior ])rofile of both valves, adult. 



Fig. 1 . Candona reptans -^-S: a, left valve ; b, dorsal profile of both valves ; 

 c, anterior profile of both valves. 



Fig. 8. Candona lucens + 8 : «, left valve ; b, dorsal profile of both valves ; 

 c, anterior profile of both valves. 



N.B. The carapace-valves and the dorsal profiles are figiu-ed with the ante- 

 rior extremity upwards ; and in the anterior profiles the dorsal 

 margins are uppermost. 



* Brit. Entom. p. 155. n. 6. tab. 18. figs. 7, 8. 



