THE TERTIARY FORMATION. 49 



No. 5. Cytherideis (?), spec. Plate VI, fig. 15. 



INCH. 



Length, ^ Lower Eocene : Kent. 



Casts of oblon go-triangular convex valves of a species probably referable to this 

 sub-genus were found by the late Rev. H. M. De la Condamine in a black clay, belong- 

 ing to the Woolwich Series, at New Cross. They somewhat resemble the more obtuse 

 forms of Cytherideis triyonalis ; but I hesitate to determine their specific relations. 



No. 6. Cytherideis Tamarindus, spec. nov. Plate III, figs. 4 a, 4 b. 



INCH. 



Length, Jy Pliocene: Suffolk. 



Carapace obliquely sub-oblong, or sub-rhomboidal, somewhat resembling a tama- 

 rind-stone in shape ; extremities obliquely rounded ; anterior extremity sloping towards 

 the dorsal, and posterior border sloping towards the ventral margin ; dorsal border 

 straight, ventral somewhat sinuous : valves depressed, most convex backwards, thick- 

 ened at the extremities, and bordered posteriorly by a narrow flattened rim ; surface 

 ornamented with a few faint concentric ridges towards the anterior and ventral 

 margins, and marked all over with a faint reticulate punctation [not shown in the 

 drawing, fig. 4]. 



Dorsal aspect elongate-compressed-ovate ; end-view narrow-subovate. 



Cythere {Cytherideis) Tamarindus is rare in the Crag of Suffolk. 



No. 7. Cytherideis Colwellensis, spec. nov. Plate IV, figs. 13 a, — 13 c, 



20 a— 20 c. 



INCH. 



Length, ^ Upper Eocene : Isle of Wight. 



Carapace oblong, most convex posteriorly ; extremities rounded, the anterior end 

 more or less obliquely ; dorsal border gently arched ; ventral nearly straight : surface 

 smooth or faintly punctate. 



Dorsal aspect narrow-acute-ovate ; end-view blunt-oval. 



Cythere {Cytherideis) Colioellensis occurs at Colwell Bay, Isle of Wight, in the 

 Nucula-bed {Nucula deltoidea) and other deposits ; but is not abundant. 



7 



