THE TERTIARY FORMATION. 15 



No. 4. Cypris gibba, Bamdohr. Plate I, fig. 3 a— fj and Woodcut, fig. 1, p. 16. 



Cypris gibba, Ramdohr. Magaz. d. Gesellsch. Naturforsch. Freunde zu Berlin, 1808, ii, 



p. 91, t. 3, figs. 13—17. 

 BIoNocuLUS BiSTEiGATUs, Jurine. Hist, des Monocles, p. 177, t. 19, figs. 12, 13. 

 Cypris biplicata, Koch. Deutschlands Crustac, &c., Heft 21, t. 16. 



— — S. Fischer. Me'm. Sav. Etrang. Petersburg, vii, p. 150, t. 5, figs. 5 — 8. 



— siNUATA, lb. Mem. Sav. Etrang. Petersburg, vi, p. 193, t. 10, fig. 4. 

 • — BiSTEiGATA, Liljeborg. De Crustaceis, &c., p. 121, t. 11, figs. 17, 18. 



— GIBBA, Jones. Ann. and Mag. Nat. Hist., 2d ser., vi, p. 26, t. 3, fig. 4. 



INCH. 



Length, ^'j Recent : England ; Europe. 



Post-tertiary : Cambridgeshire. 

 Pleistocene : Kent ; Esses. 



Carapace oblong, compressed : valves larger anteriorly than posteriorly ; rounded 

 obliquely in front ; rounded behind ; straight on the dorsal, incurved at the middle of 

 the ventral border ; marked across the middle by two unequal parallel furrows, 

 situated side by side, and strongest towards the dorsal border ; these two sulci (the 

 foremost of which often becomes obsolete) form an irregular impression which divides 

 the surface into two nearly equal, slightly gibbose portions, each of which in old speci- 

 mens is sometimes surmounted with a tubercle (Plate I, fig. 3 a). In young individuals 

 the impression is scarcely perceptible (fig. 3 e). Surface of the valves impressed with 

 closely set circular punctations (fig. 3/), which are either irregular in their disposition, 

 or follow wavy lines, rather concentric as to the two halves (anterior and posterior) 

 of the valves. Irregular pits and knobs are frequent near the middle of the adult 

 valve- 



The Jdiiffe is well seen on the smaller (right) valve, and consists of a straight, 

 simple, smooth ridge, extending nearly the whole length of the dorsal border, and 

 slightly modified at its posterior portion, where it becomes somewhat broader and 

 sulcated. The inner marginal plates of the valves are rather feebly developed. 



The recent individuals have usually a dull yellowish colour, and, like the fossil 

 forms, vary considerably both as to the extent to which the ventral border is incurved, 

 and as to the development of the vertical median sulci and their attendant pits and 

 varices, and other irregularities of the surface. 



Dorsal aspect elongate-oval or lanceolate ; anterior, ovate. 



This is a very common species in our fresh-water ponds and rivers ; but, as 

 Ramdohr has remarked [loc. cit.). it has the habit of remaining on or in the mud rather 



