THE TERTIARY FORMATION. 31 



Carapace oblong ; extremities obliquely rounded : valves thick, somewhat depressed, 

 showing more or less distinctly the central and two posterior tvibercles ; surface finely 

 reticulated, the meshes small, angular, and deep, the parietes of the meshes thick, 

 squared, and strong ; on the ventral slopes the longitudinal parietes of the reticulation 

 are the most distinct (as is usual in reticulated carapaces), on the rest of the surface 

 the reticulation is irregular or labyrinthine. 



Borsal as2:)ect narrow-obtuse-ovate ; end-view subovate. 



Cythere Didyosigma somewhat resembles C. bidentata, Bosquet (' Entom. Tert.,' 

 p. 72, t. 3, fig. 9), from Dax. It is not uncommon in the Crag of Suffolk; but the 

 specimens were overlooked when the plates were being prepared. 



No. 13. Cythere lacunosa, sj)ec. nov. Plate III, figs. 5 a, 5 b. 



INCH. 



Length, ^V Recent : Norway. 



Pliocene : Suffolk. 



Carapace oblong, slightly tapering backw^ards ; rounded obliquely at the extremi- 

 ties ; posterior lobe narrow and thickened ; dorsal and ventral edges nearly straight ; 

 valves somewhat depressed, with the centre sunken and occupied by a large tubercle ; 

 margins depressed and thickened : surface of valves marked by 3 — 4 concentric riblets 

 towards the anterior margin, one of which is continued along the dorsal part of the 

 valve ; parallel with and inside this slight dorsal ridge is a row of coarse, quadrangu- 

 lar, shallow pits ; an obscure punctation and scattered pimples occupy the middle part 

 of the valves, especially around the great central tubercle. 



Dorsal aspect irregular-narrow-oblong. 



This species occurs in the Crag of Suffolk, where it is rather rare. It is plentiful 

 in the deeply dredged shell- and sponge-sand from the Norway coast, with which I 

 have been favoured by Messrs. MacAndrew and Barrett. 



No. 14. Cythere scabropapulosa, spec. nov. Plate V, fig. 16. 



INCH. 



Length, -j'-g Middle Eocene : Bracklesham. 



Carapace sub-oblong ; tapering backwards, and ending in a flattened, angular, 

 denticulate, posterior lobe ; anterior extremity obliquely rounded, bordered by a thick- 

 ened and raised margin : surface of valves thickly beset with low and I'ounded tubercles; 

 anterior hinge marked by a strong tubercle. 



