40 BRITISH CRETACEOUS BRACHIOPODA. 



In England, T. gracilis is very abundant in the Upper and Lower Chalk of many 

 localities ; thus, at and between Dover and Folkstone, Mr. Mackie, myself, and others have 

 found it in both the Upper and Lower Chalk ; at Charing, Kent, it has been obtained from 

 the chalk detritus by Mr. Harris; likewise in the Sussex Chalk by Mr. Catt. Mr. 

 Bowerbank has it from the Chalk of Trimmingham ; Messrs. Fitch, Woodward, and 

 others, from that of Norwich ; and Mr. C. B. Rose informs me, that he has found it in 

 the Blue Gault of West Norfolk. I have not seen any specimens from the Gault of the 

 South of England, nor from either the Upper or Lower Green Sand : its vertical range 

 seems much smaller than that of T. striata. 



On the Continent, T. gracilis is likewise abundantly distributed, and its principal 

 varieties have been figured by Schlotheim, Sowerby, Rcemer, V. Buch, Geinitz, Reuss, 

 and D'Orbigny. 



Plate II, fig. 13. A specimen, with the smaller valve almost flat, very slightly convex, 



only at the umbo, from the Chalk of Trimmingham, in the 

 collection of Mr. Bowerbank. Similar specimens are also pre- 

 served in the York Museum. 

 „ fig. 14. A remarkably fine specimen, the smaller valve being almost flat, 



from the Chalk near Norwich, in the collection of Mr. Eitch. 

 „ fig. 15. The interior of the smaller valve, from Dover, in my collection. 

 ,, fig. 16. A variation, in which the smaller valve is slightly convex, from the 



Chalk of Dover. 

 „ fig. 17. A very convex variation, also from the Kentish Chalk, illustrating 

 the greatest number of striae I have noticed in the species. 



Sub-genus — Kingena, Dav. 1852. 



Animal fixed to submarine bodies by means of a pedicle; shell inequivalve, more 

 or less circular or ovate ; valves convex; beak moderately produced, recurved; foramen 

 circular, partly completed by a deltidium in two pieces, not always visible, from the foramen 

 lying close to the umbo. Structure punctuated, surface variously ornamented by granular 

 spinose or squamose unequal asperities irregularly disposed. Beak ridges well defined, 

 leaving a false area between them and the hinge margin, valves articulating by means of 

 two teeth in the larger and corresponding sockets in the other valve. In the interior 

 of smaller valve, a deep hollow crura, or muscular fulcrum, widely separates the inner 

 socket walls ; no produced boss ; a small deep depression lies along the centre of the 

 crura, giving rise to a short elevated mesial longitudinal septum not extending further 

 than half the length of the valve. On either side of the crural base two riband-shaped 

 lamellae are fixed; these, after proceeding a short distance, throw off a lateral process 

 which attaches itself to the sides of the central septum, at a short distance from its origin ; 



