LINGULA. 7 



. Diagnosis. Shell oblong, irregularly oval, slightly convex, but compressed and 

 flattened longitudinally along the middle ; valves almost equal ; beaks not very acute ; 

 truncated or rounded in front, shell thin, shining, horny; surface wrinkled by numerous 

 concentric elevated lines of growth ; more numerous at the sides. Length 13, breadth 8, 

 depth 3^ lines. 



Obs. Lingula truncata was discovered by Dr. Fitton in the Lower Green Sand of 

 Atherfield (Isle of Wight), Sandgate, and Peasemarch ; it is the largest cretaceous Lingula 

 with which I am acquainted, some specimens measuring full 1 3 lines in length. L. truncata 

 is quite distinct from Lingula ovalis, Sow., M. C, tab. xix, fig. 4, as correctly stated by 

 Professor Forbes in the ' Quarterly Journal,' vol. i, p. 346. I am now quite certain that 

 Sowerby's specimens of Lingula ovalis were obtained from the Kimmeridge Clay, found in 

 blocks at Pakefield in Suffolk, associated with other well characterised Oolitic species. 

 T. ovalis was therefore never to my knowledge found in the Lower Green Sand of 

 Sandgate, as stated by M. D'Orbigny, nor in the cretaceous period, where it is placed 

 by several authors. M. D'Orbigny's Lingula Rauliniana is only a synonym of L. truncata, 

 his description and figure quite agreeing with the specimens of that type, as any one may 

 become convinced of on examination of the original specimens now deposited in the 

 Museum of the Geological Society. 



Plate I, figs. 27-28. A specimen, natural size, from the Lower Green Sand of Red 



Cliff, Isle of Wight, in my collection. 

 „ fig. 31. From a specimen found in the Lower Green Sand, of Sandgate; 



Dr. Pitton's figures were, unfortunately, not very well illus- 

 trated, which is perhaps the reason why some authors have 

 not recognised the type. 



2. Lingula subovalis, Dav. 1852. Plate I, figs. 29-30. 



Diagnosis. Shell regularly oblong, oval, the beak and front presenting nearly the same 

 shape; valves almost equal, slightly convex, compressed; shell thin; surface smooth, marked 

 only by a few concentric lines of growth. Length 7, width 4, depth \ lines. 



Obs. This small Lingula is found in the Upper Green Sand, near Warminster, where 

 it does not seem much to exceed the dimensions above given ; it appears distinct from 

 L. truncata by its more regularly oval shape, and much smaller size, nor would it 

 seem to be the Lingula ovalis of Sowerby, which is a Kimmeridge Clay Shell, but placed 

 erroneously by most authors in the Lower Green Sand, which is the reason why I supposed 

 it so, while writing on this genus in Part III ; but this opinion I afterwards relinquished, 

 having been able to compare specimens from the two formations. We are therefore at present 

 acquainted with only two British Cretaceous Lingulas, viz., L. truncata and L. subovalis ; 

 and in the Oolitic series other two, viz., Lingula Beanii and L. ovalis. I have named 

 our shell, Subovalis, to indicate its approximation in shape to L. ovalis, Sow. 



2 



