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BRITISH FOSSIL TR1GONLE. 



shire, and in Yorkshire at Malton and Pickering ; at the two latter localities it may be 

 understood as the species intended whenever T. codetta is mentioned in lists of their 

 fossils. Specimens are in the Museum of the Royal School of Mines, in the Wood- 

 wardian Museum, Cambridge, in the Geological Museum of the University of Oxford, in 

 the museum of the Philosophical Society, York, in that of the Philosophical Society, 

 Scarborough ; also in private collections. 



Specimens from the Coralline Oolite of Weymouth are usually of smaller size, and 

 are more lengthened, or measure less across the valve at right angles to the carina, than 

 Yorkshire examples. 



In Switzerland, Agassiz records its occurrence in the same geological position at 

 Zwingen (Soleure), at which place he states that it has been obtained in considerable 

 numbers and in a fine condition of preservation. D'Orbigny also records it in the Coral 

 Rag of France at several localities. 



Trigonia Cassiope, D'Orb. Plate XXXII, figs. 1, 2, 3, 4, 5. 



Trigonia Cassiope, d'Orbigny. Prodrome de Paleont., vol. i, p. 308, 1850. 



— — Lycett. Sup. Monog. Gr. Ool. Moll. Pal. Soc, p. 49, tab. xxxvii, 



fig. 10, 1863. 



— — Rigaux and Sauvage. Descr. de quelques especes nouv. de 



l'Etage Bathonien du Bas-Boulonnais, 

 p. 19, 1868. 



— — Phillips. Geology of Yorkshire, 3rd ed., vol. i, p. 250, 1875. 



— — Judd. Mem. Geol. Survey Rutland, &c, p. 289, 1875. 



Shell variable in its general figure and outline ; ovately trigonal ; somewhat depressed 

 and comparatively short anteally ; usually considerably lengthened and attenuated 

 posteally ; anteally and also near to the umbones the valves have much convexity, the 

 general outline becoming subcrescentic. The umbones are small, moderately elevated, 

 and usually much recurved ; placed upon a line one third the length of the shell from the 

 anterior border. The anterior side is rounded and inflated, its border curves elliptically 

 with the lower border, which is lengthened and sinuated posteally ; the hinge-border is 

 lengthened i and concave, farming posteally only a slight angle with the siphonal border, 

 which is oblique and shorter than in any other British example of the section ; its posteal 

 extremity forms with the marginal carina a figure much produced and pointed. The 

 escutchon is large, depressed, and somewhat excavated, so that when a valve is placed 

 horizontally the escutcheon is scarcely seen when viewed from above ; its surface is very 

 delicately, obliquely plicated, and obscurely reticulated. The area is unusually narrow 

 for so large a species, its surface forms a considerable angle with the costated portion of 



