530 EEV. G. E. WHLDBOENE ON SOME FOSSILS 



lunule), then curving suddenly and directly forward for some 

 distance, and then coming rapidly round the very convex anterior 

 side to form the almost straight inferior margin. The posterior side 

 seems to be hounded by two nearly equal straightish lines, one coming 

 down the back of the umbo very obliquely and meeting a rather 

 longer one, which is almost at right angles to the inferior side. 

 There are indications of an angular ridge from the beak to the 

 posterior corner; but the type specimen being defective in this 

 part, it is impossible to be Certain as to these characters. 



Surface covered with about thirty rather obliquely flattened, 

 reflex, transverse ridges, separated by grooves of a similar size, 

 becoming indistinct on the beak. 



One specimen in the Sharp Collection in the British Museum, 

 from " Store 'Nine Churches, near Weedon," and others in the 

 Jermyn-Street Museum, from the Cornbrash of Appleby, Lincoln- 

 shire. 



It bears much resemblance to the huge Opts trigonalis, Sow. ; 

 but besides being distinguished by the very great difference in size, 

 the lunule seems to be deeper, the umbo more erect, and the general 

 contour more squared. 



Myoconcha unguis, n. sp. Plate XVIII. fig. 21. 



Shell elongate, oblique, recurved, flat, very massive. Hinge ex- 

 tremely developed, especially in the anterior direction, where the umbo 

 curves down to form a massive hook. External groove very well 

 marked. Margins convex superiorly, dilate behind, concave below. 

 Shell-structure extremely massive, consisting of coarse growth-layers 

 which overlap the margins, except in the posterior parts. Surface 

 slightly and irregularly convex, crossed towards the rear by the 

 upper growth-layers. 



Dimensions. Length 5| inches, breadth 31 inches. 



There is a specimen of this shell in the Bristol Museum, from the 

 Inferior Oolite of Dundry, and two similar ones in the Jermyn-Street 

 Museum from Bradford Abbas. 



It differs from old specimens of Myoconcha crassa by the extremely 

 elongated and hooked anterior extremity. The great development 

 of shell gives it a superficial resemblance to an oyster, but the 

 internal scars are very clear and typical. 



Myoconcha implana, n. sp. Plate XVIII. fig. 22, and Plate XIX. 

 fig. 5. 



Shell trigonal, very oblique and transverse, angularly convex. 

 Umbones small, subterminal, facing forward. Hinge-line very long, 

 being more than three fourths of the breadth of the shell, straight, 

 and with a groove running the whole length of its external surface. 

 Pront wing small, and very convex. Hind wing very much pro- 

 duced. Anterior margin convex. Inferior margin oblique and 

 straight. Infero-posterior corner sharply rounded. Posterior margin 

 oblique, nearly straight, meeting the hinge-line at an. obtuse angle. 



