108 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



Shell small, sub-fusiform or ovately elongated, spire elevated, volutions 5 or G, rather 

 convex ; the last volution ovate ; aperture elliptical, its base narrow ; the surface, with very 

 delicate, closely arranged, perpendicular lines, which render the surface slightly rough. 



As the outer lip is much broken in both the specimens examined, the figure of the 

 anterior extremity of the aperture is rather doubtful, and the general figure of the shell is 

 more fusiform than is usual in this genus ; the columella is rounded, and quite destitute 

 of any plication. 



Geological Position and Localiiy. The Forest Marble of Laycock ; in the collection of 

 W. Walton, Esq. 



OsTREA WiLTONENsis, Lyc. Tab. XXXIV, figs. \,\ a. 



Testa, vnha libera jjlanafa, crassa, solida, ovato-triangulari, lrevi,apicc erecto, obtuse ; 

 sidco cardinis lato, siiperjiciali. Valva affixa ignota. 



Shell with the free valve flattened, but solid and thick ; its borders are raised inter- 

 nally, rendering the inner surface somewhat concave ; the figure is ovately triangular, but 

 short, with the apex erect and obtuse; the hinge sulcus is wide and superficial. The 

 affixed valve is unknown. 



Several large specimens of this ponderous but flattened oyster have been obtained by 

 Mr. Walton, including the monstrosity, Tab. XXXIV, fig. I a. The height is greater than 

 the opposite measurement ; it has some resemblance to 0. deltoidea, but less flattened, not 

 transverse, and with the umbones not oblique ; and as the specimens are constant in their 

 general characters, there can be no doubt of its distinctness from that species. 



Geological Position and Locality. — The Forest Marble of Pound Pill. 



OsTREA (Exogyra) lingulata, Walton MSS. Tab. XXXII, figs. 2, 2 «, 2 b. 



Testa valva inferiore sublavi, excavata, elongata, postice carinata, margine antcriore 

 subrecfo, cardine brevi, antrorsuht curvato. Valva libera phmata, elongata, linguceformi, 

 umboni compresso, arcuato ; facie interne sulco longitudinali oblique instructe. 



Shell, with the affixed valve excavated, elongated, smooth, with a posterior external, 

 longitudinal angle ; hinge margin short, and curved forwards ; anterior border straight, 

 posterior border curved elliptically. Free valve flattened, smooth, lengthened, and tongue- 

 shaped, tapering towards both the extremities ; the umbo is depressed, and much curved ; 

 the inner surface with a lengthened posterior sulcation The length is usually about twice 

 the opposite diameter. 



A species allied to Exogyra carinata. Roemer Nordd, Ool., p. CC, pi. 3, fig. 15. 

 This latter, however, appears to have the affixed valve more flattened and lunulate. 



