80 THE ENTOMOSTRACA OF 



the Cretaceous deposits, except Speeton Clay ; it occurs also in a Tertiary Blue Clay 

 at Brackleshara. 



The young form of this species is described by M. Roemer, as occurring in the 

 Lower Chalk-marP at Lemforde. 



C. reniformis, Bosquet, is apparently a kidney-shaped variety of this species ; and 

 it is very probable that the var. brevis of Cythere amygdaloides^ Cornuel, is also identical 

 with C. ovata. 



No. 2. Cytherella truncata, Bosquet. Tab VII, fig. 25 a — e. 



Cythekina truncata, Bosquet. Ent. foss. Maestricht, p. 7, n. 2, pi. i, fig. 2 a — c. 



40 



Length, 

 Height, -jj 

 Thickness, 



YOUNG. ADULT. 

 INCH. INCH. 



g-'g. Gault, Folkstone andLeacon Hill. Tertiary, Eocene, Alabama, North America. 



Jq^ Chalk-marl, Dover. — — Barton, Hants. 



y^- Detritus, Charing. — — Colwell Bay, Isle of "Wight. 



Chalk, South-East England. — Miocene, Bordeaux. 



Chalk, Maestricht (Bosquet). 

 — Balsberg, Sweden. 



Carapace oblong, closely resembling in shape the seed of the sunflower ; retaining 

 the same form through all stages of growth ; occasionally constricted across the 

 median third of the valves, and subject to slight variation in the curvature of the 

 dorsal and ventral borders. Valves convex on the posterior half, depressed anteriorly, 

 smooth and shining; faintly pitted, the punctations arranged in seven to eight 

 longitudinal lines.^ Dorsal and ventral borders nearly straight. Anterior and posterior 

 extremities somewhat rounded, the latter sometimes oblique at its superior moiety. 

 The dorsal border of the right (larger) valve is more arched than that of the left, and 

 the ventral border of the left (smaller) valve rather more incurved than that of the right. 



Dorsal aspect wedge-shaped ; anterior compressed oval. 



This differs from the preceding species by the carapace being smaller, narrower, 

 and straighter ; by its being more strongly depressed anteriorly, and more decidedly 

 truncated posteriorly. 



The Maestricht form figured and described by M. Bosquet is more arcuated than 

 the generality of individuals from the other Cretaceous deposits. This species is of 

 much rarer occurrence in the Cretaceous Formation than C. ovata. The Tertiary 

 specimens are by no means rare, they vary considerably with regard to the puncta- 

 tions ; when the pittings are coarse, the specimens approach very nearly to 

 C. aciculata, Roemer (Jahrbuch, 1838, p. 517, n. 21, pi. vi, fig. 21). 



1 This " lower white (sandy) chalk-marl" is the lowermost bed of the chalk without flints, and super- 

 incumbent on the grey chalk-marl. — See Taylor's Scient. Mem. loc. cit. 



2 This character is well shown in some of the best preserved of the Gault specimens. 



