TEREBRATULA. 29 



attached to the crura, and extending to near the internal frontal margin ; impressions of 

 the posterior divisions of the valvular muscles strongly marked, valves minutely punctuated 

 and marked by numerous lines of growth. Dimensions variable, average length 14, 

 width 18, depth 7 lines. 



Obs. This species appears to have been first described and named by Lamarck, it has been 

 long known as a characteristic liasic species, and, as is the case with most brachiopoda, it 

 varies considerably in shape, and, in my opinion, passes by insensible graduations into the 

 next form distinguished by Sowerby under the name of Ter. cornuta. Some specimens are 

 so irregular that one half would present the characters of quadrijida, while the other has those 

 of cornuta. In England the type forms of quadrijida, are much more rare than those of 

 cornuta, and seem to pass into each other's type more than similar shells on the Continent, 

 and especially in Normandy, where both appear more distinct and permanent in their 

 character ; therefore, to meet the wishes of the generality of Palseontologists, both names 

 are preserved, and the following may be given as distinctive characters. T. cornuta is 

 deeper, more convex, and longer than it is wide, the reverse of what we generally find in 

 quadrijida, which is wider than it is long, flatter and much less deep, the beak and area are 

 also larger and more produced in T cornuta. Both species, or more properly speaking, in 

 my opinion, varieties of one type, they are found together in the same beds and localities, 

 but in some places one or the other form prevails. In Plate III will be seen illustrations 

 of both forms, as found in England; figs. 8, 9, 10 represent Ter. quadrijida, while 

 11 — 18 illustrates Ter. cornuta. Ter. quadrijida is usually found in the marlstone or 

 middle lias, and particularly at South Petherton, near Ilminster, where Mr. Moore pro- 

 cured many specimens, but I have not seen any as large or as fine as those of Normandy, 

 Vieuxpont, Landres, and Evrecy, near Caen ; M. D'Orbigny states their occurrence at 

 Saint- Amand (Cher.), and Nancy, in France. Pigs. 8 — 9 are from Mr. Moore's collection. 



22. Terebratula Cornuta, Sow. Plate Til, figs. 11 — 18. 



Terebratula cornuta, Soto. Min. Concli., 1825, vol. v, p. 66, pi. 446, fig. 4. 



— vicinalis, V. Buck. 1838. Mem. Soc. Geol. de France, vol. iii, p. 192, 



pi. xvii, fig. 5. (Non T. vicinalis, Schloth., according to 

 M. D'Orbigny.) 



— cornuta, Morris. Catalogue, 1843. 



— — Bronn. 1849. Index Palseont., p. 1233. 



— — D'Orb. Prodrome, 1849, vol. i, p. 240. 



Diagnosis. Shell inequivalved, irregularly pentagonal, generally longer than wide ; 

 valves almost equally convex, thick and deep ; hinge-margin forming nearly half the 

 circumference of the shell, the remaining portion and front being divided into three more 

 or less defined concave curves, the central or frontal one in common deeply indented, but 

 obscurely so laterally, the surface of both valves are smooth and shining ; three concave 

 sinuses, forming two elevated rounded ridges, visibly diverging from the umbo towards 



