﻿106 



BRITISH FOSSIL TRIGONE. 



Trigonia nodosa, Sow. Plate XXV, figs. 1, 2. Far. Orbignyana, Plate XXIV, figs. 



1, 1 a, 2, 3. 



Trigonia clavellata, Mantell. Geol. Sussex, p. 73, No. 10, 1822. 



— nodosa, Sowerby. Mineral Conchology, vol. vi, tab. 507, fig. 1, p. 7, 



1829. 



— d^idalea, Be la Beche. Geol. Manual, p. 287, 1832. 



— — Mantell. Geol. of South-east of England, p. 1 79, 1833. 

 Trigonia cincta, Agassis. Trigonies, p. 27, tab. vii, figs. 21 — 23 ; and tab. viii, 



figs. 2—4, 1840. 



— — Matheron. Catal. de Corps Org. Foss. du Depart, des Bouches du 



Rhone, p. 166, 1842. 



— rudis, B'Orbigny. Pal. Fran. Terr. Cret., pi. 289, 1843. 



— DiEDALEA, Ibbetson and Forbes. Proc. Geol. Soc, vol. iv, p. 144, 1844. 



— — Fitton. Quart. Journ. Geol. Soc, vol. iii, p. 317, 1845. 



— rudis, B" Orbigny . Prodrome de Paleont., vol. ii, p. 78, No. 291, 1850. 



— cincta, Buvignier. Statist. Geol. Miner, et Paleont. du Depart, de la 



Meuse, p. 473, 1852. 



— nodosa, Morris. Catal., p. 229, 1854. 



— — Cotteau. Moll. Foss. de l'Yonne, p. 76, 1857. 



— d.edalea, Pictet et Renevier. Foss. du Terr. Aptien de la Perte du 



Rhone et des Env. de Ste. Croix, 

 pi. xii, fig. 1, 1857. 



Shell ovately oblong, moderately convex anteally and mesially, depressed posteally ; 

 umbones small, anterior, pointed, scarcely elevated above the superior border ; anterior 

 side very short, its border curved elliptically with the lower border; superior border 

 lengthened, straight, its posteal extremity forming an obtuse angle with the siphonal 

 border of the area, which is sinuated, and its lower extremity curves elliptically with the 

 lower border. Ligament of the hinge occasionally preserved ; large, in its absence the 

 ligamental plates are conspicuous in their wide fossa. Escutcheon narrow, horizontal, 

 flattened, its surface with small, oblique, irregular, nodose elevations. Area large, 

 flattened, equal to two fifths of the surface of the valve in the variety Orbignyana, or to a 

 moiety of the surface in the typical form ; a row of nodes divides the area into two 

 portions, the superior or outer portion is the larger, and is somewhat more depressed 

 than the other, adjacent to the umbo ; the area has three conspicuous rows of large 

 depressed nodes, representing the inner, median, and marginal carinse ; the inner carina 

 has its nodes ovately lengthened, and near to the posteal extremity of the escutcheon they 

 become mere plications of growth ; the median and marginal carinas have their nodes 

 more rounded, but often somewhat concave upon their anteal sides, producing a comma- 



