TEREBRATULA. 41 



Diagnosis. Shell ovate rhomboidal, depressed when young, elongated and gibbous when 

 adult ; beak rounded, much recurved and truncated by an entire foramen closely approach- 

 ing the umbo ; deltidium in two pieces, more or less hid by the prominence of the beak, 

 without distinct lateral ridge; imperforated valve, most convex near the umbonal part 

 of the shell ; when young sometimes slightly indented in front, most wide posteriorly ; 

 rather depressed laterally, and tapering more or less in front : surface smooth, finely punc- 

 tuated : loop simply attached to the crura and extending to near the frontal margin ; form 

 variable; average size, length 16, width 11, depth 10 lines. 



Obs. Several species have been established from varieties of the type under con- 

 sideration, but they merge into one another by insensible passages ; we might probably 

 place among them Ter. lagenalis, Schl., and triquetra of Sow.; this last, especially, is only 

 a younger, wider and slightly indented state, as I became convinced from an examination 

 of the original specimens of the ' M. C lent me by Mr. J. De C. Sowerby, PL VII, figs. 

 10, 11 and 12, illustrating the original types of T. triquetra. The principal difference I 

 perceive between T. lagenalis and T. ornithocephala, is that in the last the posterior margin 

 of the shell is larger and more prominent, while in T. lagenalis the lateral sides are much 

 straighter, and wider and more square in front. Prof. Brown in his '■Index Palaontologicus' 

 places T. lagenalis among the Synonyms of ornithocephala; and M. Deshayes in 1836, while 

 describing Ter. lagenalis, states that it has some analogy to ornithocephala ; but as several 

 Palaeontologists seem desirous of retaining the name of T. lagenalis fox those more elongated, 

 thicker and straighter varieties, I have described both under a distinct head, and in PL 

 VII will be seen a number of specimens illustrating both. Figures 6, 7, 8, 9, 10, 11, 12, 

 would represent the typical forms of ornithocephala. The interior of both T ornitho- 

 cephala, fig. 23, and T. lagenalis are completely similar ; some varieties or rather specimens 

 of ornithocephala, though gibbous at the umbone, present a slight longitudinal depression 

 in that portion as seen in fig. 9. Terebratula lampas of Sow. is merely an internal cast of 

 Ter. ornithocephala, and which M. D'Orbigny seems to adopt as a species, and gives it to 

 a Liasic shell, but which I believe has nothing to do with Sowerby's type. 



In England Ter. ornithocephala is found in the Kelloway Rock, at Kelloway, where 

 it was found by Messrs. Walton, Morris, &c. : it is abundant in the Fullers-earth all round 

 Bath ; in the Cornbrash of Rushden, in Northamptonshire, where it was picked up by the 

 Rev. A. W. Griesbach, &c. ; and may be seen in the Collection of the British Museum, 

 as well as in most collections. It is also found in many parts of the Continent. 

 Count A. De Zigno mentions it from the Venetian Alps; Zeiten and Quenstedt in Germany ; 

 and Deslongchamps from Normandy. PL VII, figs. 7, 8, in British Museum; figs. 10, 11, 

 the original specimens of T. triquetra, in the Collection of Mr. J. De C. Sowerby ; fig. 23, 

 interior, from the Collection of Mr. Morris. 



