﻿SCABR^E. 



139 



Upon the whole, well-preserved specimens of T. spinosa rank with the rarer 

 Testacea of the Greensand. No specimen obtained at any foreign locality has come under 

 my observation. 



Trigonia ornata, D'Orb. Plate XXIV, figs. 6, 7. 



Trigonia spinosa, Be la Beche. Geol. Manual, p. 287, 1832. 



— — Mantell. Geol. South-east of England, p. 179, 1833. 



— orn ata (spinosa, var.), Fitton. Stratigraphical Section in the Isle of Wight, 



Quart. Jour. Geol. Soc, vol. Hi, No. 11, 

 p. 289, fossil No. 65, 1847. 



— — B'Orbigny. Prodr. de Paleont., vol. ii, xvii, Stage, p. 106, No. 709, 



1850. 



— — — Pal. Fran., Terr. Cret.,3,p. 136, pi. 288, figs. 5-9, 1843. 



— — Morris. Catalogue, p. 229, 1854. 



— — Bidet. Paleont. Suisse, vol. i, pi. xii, fig. 4, 1857. 



Shell sublimate or crescentric, convex ; umbones antero-mesial, prominent, obtuse, 

 and recurved; anterior and lower borders rounded elliptically ; hinge-border short, 

 somewhat concave, sloping downwards, and forming a distinct, obtuse angle with the 

 posteal border of the area, which is of moderate breadth and terminates downwards, 

 forming a right angle with the lower border of the valve. In conformity with the con- 

 siderable convexity of the shell the area is much curved ; it is of moderate breadth ; it 

 has a slight median furrow ; its inner and outer border are rendered conspicuous by the 

 terminations of its transverse costellae, which are large, slightly waved, and striated. 

 The escutcheon is of moderate breadth, much excavated outwardly ; its superior border 

 is raised ; it is traversed by transverse costellae similar to those of the area ; together 

 with the area the posteal or superior surface forms a considerable angle with the other 

 portion of the valve. The costae are numerous (about twenty-one), large, rounded, and 

 closely arranged ; they are somewhat less numerous than the costellse upon the area, the 

 extremities of which they meet at the prominent dividing ridge or angle of the valve, with 

 which they form an angle greater than a right angle ; they pass downwards, nearly in a 

 straight direction, enlarging rapidly about the middle of the valve, and then curving 

 forwards gracefully ; they curve somewhat upwards as they meet the anterior border ; 

 the last-formed seven costse diminish in size symmetrically, and pass almost perpen- 

 dicularly dowmvards to the lower border ; the costae have their sides regularly plicated, 

 forming rounded elevations upon the summits of the costae. Its nearest ally is T. 

 Archiaciaua, compared with which it has greater convexity ; the umbones are much more 

 prominent and are more recurved ; the area has less breadth and forms a greater angle with 

 the other portion of the valve ; the costae are different in figure ; their anteal enlargement 



