RHYNCHONELLA. 81 



2 or 3 in the smaller valve forming an elevated mesial fold, with 1 or 2 in the sinus. 

 Surface minutely longitudinally striated; the concentric lines of growth intersecting the 

 striae so closely, as to give them a squamose wrinkled aspect, especially as they become more 

 defined and projecting towards the margins. Length 8J, width 9^, depth 7 lines. 



Obs. This species belongs to the Kimmeridge Clay, of Pottern, Wilts, where it was 

 found by Mr. Cunnington, and bears so great an external resemblance to some varieties of 

 B. variabilis, Schl., that we might easily mistake it for that species; but, on examining with 

 care the structure of the shell under notice, we find that, besides the larger costae, the 

 surface is longitudinally striated, and intersected by closely and roughly disposed squamose 

 concentric lines of growth. 



The examples figured are from the collection of Mr. Cunnington, three of which may 

 be likewise seen in the British Mnsenm; from not having had the two specimens at the 

 same time, we were obliged to figure them in different plates, the last one, PL XVIII, 

 fig. 11, presented only two plaits on the sinus, while the one figured in PL XV, fig. 7, 

 possesses three. 



73. Rhynchonella Lycettii, Dav. Plate XV, fig. 6. 



Diagnosis. Shell inequivalved, transversely oval, wider than long, beak produced, 

 rounded, slightly recurved at its extremity, foramen circular, entirely surrounded by the 

 deltidial plates; beak ridges well defined, leaving between them and the hinge margin a 

 flat space or false area not indenting the smaller valve. The imperforated valve is regularly 

 convex from the umbo to the front, the deepest portion of the shell being towards the 

 middle, surface ornamented by eleven or thirteen large and deep costae, three of which form 

 a mesial fold elevated above the lateral plaits, and corresponding with two in the sinus of 

 larger valve. The edge in some specimens is thickened, forming a receding margin all 

 round, so that the extremity of the plaits project further than the junction of the valves. 

 Structure unpunctuated. Length 11, width 13, depth 7 lines. 



Obs. This species seems distinguished from B. variabilis by its more transversely oval 

 shape and rounded beak, it was discovered by Mr. Lycett in the middle division of 

 the Inferior Oolite of Minchinhampton, where it is very rare. 



Fig. 6. From the collection of Mr. Lycett. 



74. Rhynchonella oolitica, Dav. Plate XIV, fig. 7. 



Diagnosis. Shell irregularly triangular, nearly as wide as long ; beak acute, and not 

 much recurved, leaving a flat, false area between its ridges and the hinge margin ; foramen 

 small, circular, entirely surrounded, and separated from the umbo by the deltidial plates; 



