﻿140 BRITISH FOSSIL TRIGONLE. 



and posteal attenuation and slight sinuation upwards towards the angle of the valve are also 

 distinctive features. The costellated, wider, and flattened area serves to separate it 

 from T. crenulata and also from the little T. Vediana, which is much more produced 

 and attenuated posteally ; the apices are also far more recurved. 



StratigrajMcal position and Localities. T. ornata occurs somewhat rarely in the Perna 

 bed of the Neocomian formation at Atherfield ; the valves are disunited ; the test is 

 preserved. At Hythe the Neocomian Sandstone has produced it in great profusion, for 

 the most part indifferently preserved and flattened from pressure. 



France: St. Dizier, Vassy, Aucerville, Auxerre, Perte-du-Rhone (Ain). 



Note. — In the introductory portion of the present Monograph, p. 8, T. Picteti, Coq., 

 is mentioned as one of the British species ; the subsequent acquisition of uncompressed 

 examples of T. ornata, with the test preserved, has convinced me that our specimens 

 should be referred to the latter species. It may also be remarked that the figures of 

 T. ornata given in the ' Paleontologie Frangaise ' are not good representations of British 

 specimens, and that the figure in Pictet's work is a much nearer approximation to 

 them. 



Trigonia Archiaciana, D'Orb. Plate XXIII, fig. 7 ; Plate XXV, fig. 10 (mould). 



1 Trigonia pumila, Nilsson. Petref. Suec, tab. v, fig. 7, 1827. (Young example.) 



— SPINOSA, Sotoerbtj. Geol. Trans., 2nd ser., vol. iv, pi. xiii, fig. 3, p. 338, 



1836. 



— — Agassiz. Trigonies, p. 30, tab. vii, figs. 4-6, 1840. (Mould.) 



— Archiaciana, B'Orbigny. Paldont. Fran., Terr. Cret., vol. ii, pi. 290, figs. 



6, 8, 10, 1843. 



— — Pictet et Roux. Descr. Moll. foss. Gres vert, pi. xxxv, 



fig. 4, 1847. 



— — B'Orbigmj. Prodrome de Paleont., vol. ii, p. 137, No. 241, 



1850. 



— — Morris. Catalogue, p. 228, 18.54. 



— — Pictet et Renevier. Pale'ont. Suisse, Terr, aptien de la 



Perte-du-Rhone et des Env. de St. 

 Croix, p. 95, pi. xli, fig. 3, 1857. 



Shell with nearly the general outline and figure of T. ornata, but smaller, with the 

 umbones more pointed and less recurved ; the general convexity is also less ; the area is 

 more expanded, its surface forming a smaller angle with the surface of the other portion 

 of the valve ; the costae are elevated, but narrower and more closely arranged than in 

 T. ornata ; they curve with great regularity obliquely downwards and forwards, but are 

 without the sinuation which their attenuated carinal portions form in T. ornata — a feature 

 which characterises that species. The divisional line of the valve forms a distinctly 



