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BRITISH FOSSIL TRIGONLE. 



Larger than T. aliformis, it is so much inflated anteally that the diameter through the 

 united valves is equal to their height and greater than their length in adult specimens ; 

 the umbones are remarkably large and arched inwards. The anteal varices (about ten) 

 are large, oblique or almost perpendicular, each fringed with a row of depressed, oblong, 

 or sometimes ovate nodes.. The posteal varices (about eight) are small, narrow, closely 

 arranged, and perpendicular ; the area is convex, plain, and bipartite ; the escutcheon is 

 very wide and boat shaped, with a few transverse costellae. It occurs very abundantly 

 at several localities on the Sunday's and Zwartkop Rivers, associated with a con- 

 siderable fauna, including the two gigantic species of Trigonia, T. TIerzogii, Haussman, 

 and T. conocardiformis, Krauss, which are also exceedingly abundant. The former 

 of these is well known from the excellent figure of it in the great work of Goldfuss 

 (' Petref.,' tab. 137, fig. 5); of this the British Museum has an unusually fine series 

 of specimens numbered 46,461. 



More recently, a considerable number of fossils from South Africa having been 

 added to the rich collection in the Museum of the Geological Society, Mr. R. Tate com- 

 municated a memoir descriptive of them and of their distribution (' Quarterly Journal 

 Geological Society/ vol. xxiii, part 3, p. 139, 1867). The comparison of these African 

 forms with their supposed European analogues has led to his assigning them to 

 the Lower Oolitic rocks, but with the reserve which should always qualify conclusions 

 deduced from comparisons of fossils so remote geographically. Admitting the general 

 apparent Jurassic fades of certain fossils figured in the plates illustrating Mr. Tate's 

 memoir, I am nevertheless much impressed by the presence in such considerable numbers 

 of Trigonia Herzogii and T. ventricosa, the former an elongate example of the 

 Quadrates, the latter of the Scabrce, sectional forms which in Europe, Asia, and 

 America, are special to and eminently characterise the Cretaceous rocks. T. 

 ventricosa more especially is nearly allied to, and possibly is not really distinct as a 

 species from, T. tuberculifera, Stol., from the Cretaceous rocks of Southern India (' Mem. 

 Geol. Survey of India,' vol. iii, pi. xv, figs. 10 — 15, p. 335). A comparison of these 

 figures of Dr. Stolicza with the very numerous specimens of T ventricosa in the British 

 Museum indicates even a closer affinity than would be looked for, judging from the 

 single specimen of the latter the subject of our wood-engraving ; the nodes upon the 

 larger varices occasionally have all the roundness and distinctness which characterise the 

 Indian species. 



Another form allied to T. ventricosa is a short inflated shell, T. Delafossei, Leymerie, 

 from the Cretaceous rocks of Spain (" Mem. sur un nov. type Pyreneen," 1 Mem. Soc. Geol. 

 de France,' 2 ser., torn, iv, pi. viii, fig. 27). This latter form is even shorter and more 

 inflated than the South African fossil ; its anteal or larger varices are each fringed with a 

 row of separate rounded tubercles ; their direction is more oblique than in T ventricosa. 

 The other gigantic Trigonia associated with T. Herzogii in Southern Africa is T. cono- 

 cardiformis, Krauss, inadequately represented in the reduced figures given by that 



