6 Mr. T. Davidson on the Brachiopoda 



1. Terehratula sinuosa, Brocchi, sp. PI. I. figs. 1-7. - 

 Anomia sinuosa, Brocchi, Conchiologia Fossile, vol. ii. p. 468 (1814), and 



(for figiu-e) Bruguiere, Eucyclopedie Methodique, tab. 239. fig. 6 a, b 



(1789). 



Sp. char. Shell ovate, longer than wide, greatest width towards 

 the middle ; valves almost equally deep, uniformly convex from 

 the beaks to about the middle of the shell, after which the dorsal 

 valve becomes more or less prominently biplicated, with a sinus 

 separating the two rounded ribs. In the ventral valve, a more 

 or less apparent median elevation is margined by depressions or 

 grooves of greater or less depth, and which correspond with 

 the median sinus and ribs of the opposite valve ; lateral mar- 

 ginal line forming a gentle and regular curve, which becomes 

 more or less biplicated in front. Beak rounded, incurved, and 

 truncated by a large circular foramen, which is partly margined 

 by a concave deltidium ; beak-ridges distinct only in the conti- 

 guity of the foramen. Surface smooth, marked only by con- 

 centric lines of growth. In the interior of the dorsal valve there 

 is a very short simple loop, not much exceeding a fourth of 

 the length of the valve, and confined to the posterior portion of 

 the shell : this loop is attached by its crura to the hinge-plate, 

 the two riband-shaped lamellae being soon united by a transverse 

 lamella bent upwards in the middle. Shell- structure punctured. 

 Proportions very variable : a large specimen measured in length 

 3 inches, width 2 inches 7 lines, depth 1 \ inch. 



Obs. It is exceedingly difficult to specifically discriminate be- 

 tween some of the many biplicated Terehratuhe which occur so 

 abundantly in the Jurassic, Cretaceous, and Tertiary formations ; 

 and I must admit that it would be impossible for me to find 

 words wherewith to distinguish the shell under description from 

 certain allied forms which occur in the above-named formations*. 



* I have seen and possess several examples of T. perovalis, T. inter- 

 media, T. biplicata, Sow., &c., which, although in all probability specifi- 

 cally distinct, agree very closely in external form with some examples of 

 T. ampulla and T. sinuosa. Nor will it be out of place to remark that 

 many specimens of T. sinuosa from Palazzo in Tuscany do exactly agree 

 in size and shape with Brocchi's description and figure of T. biplicata ; 

 and we should have felt disposed to consider them synonymous had not 

 MM. Saemann, Triger, and E. E. Deslongchamps assured us (in a paper 

 read before the Geological Society of France on the 16th of December 

 1861) that the original specimen upon which Brocchi had founded his 

 T. biplicata was derived from the Jurassic period. I, however, quite con- 

 cur with what M. E. E. Deslongchamps subsequently stated, at p. 136 of 

 his excellent monograph of the Jurassic Brachiopoda of France, viz. that 

 the imperfect preservation of the beak of Brocchi's original (?) example of 

 T. biplicata, as well as the uncertainty connected with its origin, makes it 

 desirable that the terms T, biplicata and T. indentata, as applied by 

 Sowerby, should be retained, and that the nomenclature should not be 



