﻿116 



BRITISH FOSSIL TRIGONE. 



Trigonia aliformis, Park. Plate XXV, figs. 3, 3 a, 4, 4«, 5, 6. 



Trigonia aliformis, Parkinson. Org. Remains, vol. iii, p. 1/6, tab. xii, fig. 9, 1811. 



— aliformis, Sowerby. Mineral Conchology, vol. iii, tab. 215, 1818. 



— aliformis, Deshayes. Coq. car., p. 33, tab. x, figs. 6, 7, 1831. 

 Lyriodon aLjEFORME, Bronn. Leth. Geog., vol. ii, p. 700, tab. xxxii,fig. 15, 1837-8. 

 Trigonia aliformis, Pusch. Polens Palaontologie, p. GO, 1837. 



— aliformis, Fitton. Quart. Journ. Geol. Soc, vol. iii, p. 289 (pars), 1843. 



— — Agassis. Trigonies, p. 31, tab. vii, figs. 14—16, tab. viii, fig. 12, 



1840. 



— aliformis, Morris. Catalogue, 2nd ed., p. 228 (pars), 1854 ; exclude 



L. G. S. of Sandgate and Boughton. 



— aliformis, Pictet. Paleont. Suisse, torn, i, pi. xiv, fig. 1, 1857; exclude 



fig. 2. 



Exclude the following figures of Trigonia named T. aliformis : 



Leopold de Buch, Petrefacta recuillies en Amerique, par A. de Humboldt et par Ch. 



Degenhardt, fig. 10, 1839. 

 Forbes, Geol. Trans., 2 ser., vol. vii, part iii, p. 151, 1846. 

 D'Orbigny, Pal. Fran., Terr. Cret., vol. iii, p. 143, pi. 291, figs. 1—3. 

 Lyroden aliforme, Goldfuss, Petref., vol. ii, tab. 137, fig. 6, 1836. 

 Pictet and ltoux, Gres Vert, pi. xxxv, figs. 2 a, b, 1847-53. 



Pictet and Renevier, Terr. Aptien de la Perte du Rhone, pi. xiv, fig. 2, 1857. (Fig. 1 

 is from a Blackdown specimen.) 



Trigonia aliformis is placed at the head of the first group ; it is characterised as 



follows : 



Shell sublimate, inflated anteally, produced, attenuated and depressed posteally ; 

 umbones much elevated, antero-mesial, pointed, much recurved and incurved ; anterior 

 side produced, its border rounded ; lower border rounded, but somewhat excavated 

 posteally; hinge-border lengthened, concave,. terminating posteally in a rostrated and 

 attenuated extremitjr ; ligamental aperture narrow, inter-umbonal. Escutcheon 

 lengthened, deeply concave, occupying the entire upper surface of the shell; its superior 

 or inner border is plain and much raised ; its outer border is formed by a narrow, 

 elevated, and rounded area ; it is traversed transversely or obliquely by numerous closely 

 arranged, small, serrated costellae, which are prominent near to the umbones, but become 

 only faintly traced posteally. The area is very narrow, raised, and convex ; it is 

 rendered bipartite throughout its entire length by a deep groove and its superior or 

 umbonal portion has a few small, ridge-like, transverse costellse ; the remainder of its 

 length has small, irregular, transverse plications. 



The other portion of the surface has a numerous series of costae, which originate at 



