﻿SCABR^. 123 



T. aliformis, Agassiz, ' Trigonies/ tab. vii, figs. 14 — 16 ; also tab. viii, fig. 12, both 

 represent British specimens. 



In fine, it results from the foregoing comparisons of analogous forms, that I have been 

 unable to discover any example of Trigonia aliformis obtained at any foreign locality ; 

 also that the few figures given by foreign authors, which are correctly attributed to that 

 species are delineations of British specimens. 



Trigonia Vectiana, Lye. Plate XXIV, figs. 10, 10 a, 10 h, 11; Plate XXV, 



fig. 7. 



Trigonia ALiEFORMis, Mantell. Geology of Sussex, p. 73, No. II, 1822. 



— ? PLic.ATA, Agassiz. Trigonies, p. 33, pi. x, fig. 11, 1840. (Specimen 



deprived of the test.) 



— ALIFORMIS, Ibbetson and Forbes. Proc. Geol. Soc, vol. iv, part ii. Table to 



face p. 414, 1844. (Fossils of the 

 Perna Band.) 



— ALIFORMIS, Fitton. Stratigraphical section from Atherfield to Black Gang 



Chine; Table opposite p. 289 (fossil No. 64, bed 

 No. 45), Quart. Journ. Geol. Soc, vol. iii. No. 11, 

 1847. 



— ALiroRMis, Picfet et Renevier. Foss. du terr. Aptien de la perte du Rhone, 



et des Env. de St. Croix, 1857, pi. xiv, 

 fig. 2 o, 6 c; exclude fig. 1, which is a 

 Blackdown specimen of T. aliformis. 



— — Jiidd. On the Punfield Formation, Quart. Journ. Geol. Soc, 



p. 220, 1871. 



One of the Scabrm allied to T. aliformis, and possessing a considerable general 

 resemblance to that species ; it has been mistaken for it by several palaeontologists — by 

 Mantell, by Fitton, also by Ibbetson and Forbes, and more recently by Pictet and 

 Renevier. In addition to possessing well-marked palseontological distinctive features, it 

 is also separated from the other species by its stratigraphical position, which is limited 

 to the Neocomian formation. Its diagnostic features are as follows ; — Umbones 

 considerably incurved and recurved, or not erect ; the middle and anteal portions of the 

 valves are without that sudden inflation which in T. aliformis contrasts so strongly 

 with the abrupt flattening of the attenuated portion of the valve posteal to it ; the costse 

 or varices diverge symmetrically from the angle of the valve with great regularity 

 obliquely downwards, with a slight sinuation towards the angle of the valve and regular 

 curvature; the summits and sides of the costse are strongly, closely, and regularly 

 crenulated ; they therefore fonn a well-marked contrast to the faintly marked and 

 unequal crenulations of T. aliformis, which are also limited to the summits of the costse. 

 The escutcheon possesses features equally distinctive; it has throughout its length a 



