THE CRETACEOUS FORMATION. 17 



Variety y. 



Greensand, Farringdou. 



A mutilated valve of this species, from the Coralline bed at Farringdon, exhibits 

 a surface covered with longitudinal lines of punctations, much smaller than those of 

 the Charing specimens. 



No. 2. Cythereis Gaulttna, nohis. Tab. II, fig. 7 a — c. 



INCH. 



Length, ^V 



Height, ^ Gault, Folkstone. 



Thickness, -j-i^ 



Carapace nearly oblong, somewhat foot-shaped. Valves depressed. Anterior ex- 

 tremity rounded, edged with coarse spines ; posterior contracted, coarsely spined. 

 Dorsal and ventral margins nearly straight. A little within the anterior and posterior 

 margins respectively, the surface of the valve is raised into coarse, semicircular ridges, 

 following the outline of the extremities. The central surface rises into a low four- 

 sided pyramid. The whole surface exhibits a beautiful arrangement of shghtly raised 

 network ; the meshes are irregularly hexagonal, and occupied by a slight depression 

 with a little central pit. The reticulations are cut across abruptly at the extremities, 

 and the parietes of the meshes are there prolonged into coarse, obtuse spines. The 

 hinges are slightly developed. 



This rare and pretty little species occurs only in the Gault. 



No. 3. Cythereis macrophthalma. Bosquet. Tab. II, fig. 8 a—V". 



CiPEiDiNA MACROPHTHALMA, Bosquet. 1847. Ent. foss. Maestricht, p. 16, n. 10, pi. iii, 

 fig. 3 a — d. 



INCH. 



Length, -g\ 



Height, -gL Chalk, Norwich. 



Thickness, ^a„ 



Chalk, Maestricht {Bosquet). 



Carapace-valve somewhat oblong ; irregularly gibbous ; anteriorly obliquely rounded ; 

 posteriorly subacute. Dorsal margin more or less arched ; ventral nearly straight. The 

 valve bears an irregular marginal ridge, broad and convex on the dorsal border, narrow 

 or obsolete elsewhere. The central tubercle is large and irregular, extending back- 

 wards. The hinges are very strongly developed. 



This species is very rai'e, two odd valves only being found in the Soft Chalk at 

 Thorpe, near Norwich : it is described by M. Bosquet as occurring at Sichen. 



