52 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



offered in Plate X. Under favorable circumstances this species attained considerable 

 dimensions, and is the largest Oolitic brachiopoda with which we are acquainted. These 

 larger forms have been by some believed separable from T. perovalis, and long known 

 under the name of T. ovoidea, but as we can trace every stage of growth and variation, from 

 Sowerby's type to the large specimens in the same beds and localities, it is evident 

 they must all belong to the same species, variable from the presence or nonpresence of 

 the two frontal ridges described above. The same has been observed relative to 

 T. maxillata, where, under favorable circumstances, that as well as other species have 

 attained dimensions far exceeding those of the original type. We are indebted to that 

 excellent observer, M. Deslongchamps, for the knowledge of the internal loop of this, as well 

 as of other forms, worked out with the greatest skill and patience, we perceive that in 

 this as in most species where the loop is short, the lamella becomes much wider and 

 stronger than in those where the process extends to near the frontal ridge. T. perovalis 

 is a common and characteristic fossil of the Inferior Oolite, both in England and on the 

 Continent. The largest and finest specimens have been obtained from Dundry, Dinnington, 

 Yeovil, &c, the best species being preserved in the Collections of the Bristol Institution, 

 British Museum, &c. Ter. perovalis is also very abundant in Normandy, where specimens 

 three inches in length have been procured, as may be seen in the Ecole des Mines of Paris, 

 and in the Collection of M. Tesson, of Caen, &c, and, although a well characterised 

 species, it has often been mistaken by many Geologists and Palaeontologists, who refer to it 

 forms perfectly distinct, as may be seen by the synonyms given of it. Thus Von Buch 

 thinks Ter. insignis (Schiibl) to be a variation of this species, but from which it completely 

 differs, its deltidium being formed of one piece, while in T. perovalis it is divided in two, 

 besides many other distinctions, which we shall notice under that species. Fig. 1, 2, from 

 the Collection of Mr. J. de C. Sowerby ; fig. 4, from that of Mr. Moore. 



49. Terebratula intermedia, Sow. Plate XI, figs. 1 — 5. 



Terebratula intermedia, Sow. 1812. Min. Con., vol. i, p. 48, tab. xv, fig. 8. 



Diagnosis. Shell inequivalved, obtusely five-sided, longer than wide ; beak rounded, 

 recurved, and obliquely truncated by a rather large foramen, slightly overlaying the umbo, 

 and concealing the deltidium in two pieces ; lateral ridges indistinct ; imperforated valve 

 less convex than the other, with (sometimes without) two rounded costae, commencing 

 about the middle, and continued to the margin, with a mesial furrow or sinus, and two 

 lateral ones ; front margin moderately sinuated ; surface smooth, punctuated ; loop short 

 and simply attached to crura, extending to less than half the length of the shell. Length 

 23, width 18, depth 13 lines. 



Obs. Sowerby's figures in the ' Min. Con.' do not illustrate this species in a satis- 

 factory manner, which has been the cause of many mistakes, as it is evident most authors 

 have not understood the shells intended as types, of which I became convinced from 



