216 SUPPLEMENT TO THE BRITISH 



so closely that it is questionable whether it can be satisfactorily distinguished. A large 

 specimen in Mr. Walker's collection measured — 

 Length 9, breadth 10, depth 6 lines. 

 In England it has been found by Mr. Walker in the Lower Calcareous Grit (a friable 

 yellow rock) at Castle Howard, in Yorkshire. Both the rock and specimens agree com- 

 pletely with those found in about a similar stratigraphical position at St. Remi, Ardennes, 

 in France. It is also stated by Mr. Walker to occur at Eiley, on the Yorkshire coast, in 

 the Passage-beds of the Lower Calcareous Grit, and at Appleton, near Malton. 



221. Rhynchonella Leedsii, Walker, MS. Sup., PI. XXVIII, fig. 17. 



Shell spherical, almost circular, nearly as long as broad ; valves very convex. Dorsal 

 valve evenly convex to within about two thirds of its length, when a broad mesial fold 

 commences to rise, but very slightly above the regular convexity of the valve. The 

 sinus in the dorsal valve is wide and shallow ; beak small, pointed, incurved ; foramen 

 slightly separated from the hinge-line by narrow deltidial plates. Surface ornamented 

 with about thirty small angular ribs or plaits, of which eight or nine occupy the fold and 

 sinus. A large example measured — 



Length 1\, width 8, depth 6 lines. 



Obs. — As observed by Mr. Walker, Rh. Leedsii differs considerably from Rh. varians 

 in being a rounder and more globose shell. In full-grown examples the ribs become 

 obsolete on the umbone and beak, and the beak-ridges are less strongly marked. In 

 profile also Rh. Leedsii forms a regular convex curve, while in Rh. varians the curve is 

 regularly convex at the umbone, and to about half the length of the valve, when it 

 becomes slightly concave, becoming more elevated and convex again near the front. 



Mr. J. E. Walker has named this species after his friend C. E. Leeds, Esq., M.A., 

 Oxford, who has been working at the palaeontology of Peterborough, where he has found 

 some new Reptiles. Rh. Leedsii is a common shell in the Cornbrash of Yaxley, near 

 Peterborough, and was also met with by Messrs. Leckenby and Walker in the same 

 formation near Scarborough, in Yorkshire. This species has been confounded with 

 Rh. varians and other Oolitic species of Rhynchonella. 



222. Rhynchonella egretta, E. Besl. Sup., PI. XXVIII, fig. 23. 



Rhynchonella egketta, E. Besl. Bull. Soc. Linn, de Normandie, vol. iii, pi. iv, 



figs. 4 to 6, 1859. 



