42 BRITISH FOSSIL TRIGONLE. 



in the direction of the lower border. The first formed five or six costae are more straight 

 and oblique; each has its upper terminal tubercle unusually large and elevated. 



The height is equal to two fifths of the length, and is one fifth greater than the 

 diameter across the superior border. 



This is the most elongated of the clavellatce ; the great length and horizontal direction 

 of the superior border readily separates it from T. Voltzii and from T. incurva ; others 

 of the section are more remotely allied. 



Stratigraphical position and localities. Both the specimens figured upon Plate VII 

 were obtained by Mr. Mansell in the Kimmeridge Clay of Kimmeridge Bay, Dorset. The 

 broken specimen has the area somewhat compressed or spread upwards ; it has also 

 occurred in the same formation near to Ely, and in the vicinity of Westbury, Wilts. 

 France, Boulogne-sur-Mer. 



Trigonia incurva, Benett. Plate IX, figs. 2, 3, 4, 5, 6. 



Trigonia incurva, Etherelda Benett. Catalogue of Organic Remains of Wilts., 1831, 



pi. xviii, fig. 2. 



— — Sowerby. In Fitton. Geol. Trans., 2nd ser., 4, 1836, tab. xxii, 



fig. 14 (internal mould). 



— — Brown. Index Paleontologie, 1848, p. 1280. 



— — IfOrbxgny. Prodrome de Paleont., 2, p. 60. 



— — Morris. Catalogue, 1854, p. 228. 



— — Cotteau. Etud. sur les Moll. Foss. de la Yonne, fasc. 1, Prodrome, 



1853-7, p. 76. 



— — Oppel. Juraformation, p. 721, 722, No. 145. 



— — Damon. Geol. of Weymouth Suppl., 1860, pi. vii, fig. 1 (internal 



mould). 



— Heberti, Munier Chalmas. Bull, de la Soc. Linn, de Normandie, vol. ix, 



1863—4, pi. iv, fig. 5. 



— incurva, Hebert. Note sur la Terr. Jurassique da loulonnais ; Bull. Soc. 



Geol. Fr., 2nd ser., t. xxiii, p. 214, 1865, p. 220. 



— — Pellat. Bull. Soc. Geol. de Fr., 3rd ser., 1866, t. xxiii, p. 226. 



— — P. de Loriol et E. Pellat. Monogr. Paleont. et Geol. de l'Etage 



Portlandien des environs de Boulogne- 

 sur-Mer, 1866, pi. viii, fig. 3. 



Shell elongated, curved at the two extremities or sublunate; anterior side convex; 

 posterior side lengthened, curved, depressed ; umbones large, obtuse, elevated, somewhat 

 recurved, and placed near to the anterior border, which is curved elliptically with the 

 lower border. Escutcheon concave, lengthened ; its superior border is somewhat raised. 



