TEREBRATULA. 51 



of different species. PL IX, fig. 3, from the Collection of Mr. Morris ; fig. 4, in British 

 Museum ; fig. 9, from the Collection of Mr. Bowerbank. 



Var. Submaxillata, Morris. Plate IX, figs. 10 — 12. 



The shell which I here place as a variety of Ter. maxillata would appear to some 

 Palaeontologists specifically different, but after a long and minute examination of a 

 considerable number of specimens, I came to the conclusion that the distinctive characters 

 were not sufficiently well defined or important to require it to be thus widely separated. 

 This variety is found in a light-yellow clay bed of the middle division of the Inferior Oolite 

 along with Ter. plicata, fimbria, and other well-characterised species. Var. submaxillata 

 is more pentagonal in form than what we observe commonly in maxillata, the posterior 

 portion of the shell is straighter, tapering, and less circular than is generally seen in 

 Sowerby's type ; the young state, in both species and variety, is exactly similar. 



Many fine specimens of this variety are preserved in the Collections of Dr. Wright, 

 Professor Buckmann, Messrs. Lycett, Morris, and others, who kindly forwarded to me these 

 specimens. Pigs. 10 and 12, from the Collection of Prof. Buckman ; fig. 11, from that 

 of Dr. Wright. 



48. Teeebratula Perovalis, Sow. Plate X, figs. 1, 6. 



Terebratula perovalis, Sow. Min. Con., 1825, vol. v, p. 51, t. 436, figs. 2, 3. 



— — Deslongchamps. 1837. Soc. Linn, de Normandie. 



— — V. Buck. 1838. Mem. Soc. Geol. de France, vol. iii, V" 



Serie, p. 221, pi. xx, fig. 2. 



— — Morris. Catalogue, 18-13, p. 135. 



— — Bronn. 1849. Index Paloeont, p. 1245. 

 _ _ D'Orb. 1849. Prodrome. 



Diagnosis. Shell inequivalved, ovate, longer than wide, greatest width towards the 

 middle. Cardinal and lateral marginal line forming a gentle and regular uninterrupted 

 curve, with or without two more or less defined rounded ridges in frontal portion, hardly 

 perceptible in the adult state, where the sinus separating the two ridges is filled up by the 

 convexity of the valve extending to the frontal margin, and presenting one large elevation, 

 with two lateral sinuses more or less indented. Rostral valve convex, with depressions 

 corresponding to the elevations in the smaller valve ; beak rounded and truncated by a 

 large entire foramen, nearly touching and projecting over the umbo, generally concealing 

 the deltidium ; lateral ridges indistinct, surface smooth and punctuated ; loop simply 

 attached to crura, and short, extending to only about two fifths of the length of the valve. 

 Length 33, breadth 28, depth 23 lines ; the average dimensions are much less. 



Obs. The original specimens described by Sowerby in the ' Min. Con.,' and of which 

 I have given correct figures, Plate X, figs. 1, 2, would hardly convey an idea of the species 

 under consideration, which varies considerably, as may be seen from the several illustrations 



