of the Chalk Formation. 385 



gonite, of about 2^ inches in size, as well in France as in England 

 and America. This is also the case with the Mexican Trigonia, 

 described (Bulletin de Bruxelles, torn. vii. no. 10) by MM. Nyst 

 and Galeotti, which they have named TV. plicato-costata. It is 

 not distinct from the Trigonia crenulata of Lamarck and Agassiz, 

 and when of the same size has the same number of ribs on the 

 side. When thus limited and again referred to the oldest name 

 proposed by Sowerby of Trigonia aliformis, this remarkable Tri- 

 gonia is dispersed over the whole extent of America, and every- 

 where characterizes the middle chalk. Even the Trigonia tho- 

 racica described by Morton from Alabama is now recognized by 

 him as Trigonia aliformis. M. Galeotti relates that the Trigonia 

 discovered and published by him occurs in the marls of a very 

 extensive limestone formation in the middle of the great and 

 principal Cordillera of Anahuac, twelve French miles W.N.W. 

 from the town of 'Tehuacan in the district of Puebla, and four to 

 seven thousand feet above the sea level. In that place it is so 

 abundant and large that it may be considered the chief and most 

 characteristic fossil of the whole formation. It is wonderful, says 

 Galeotti, to find in one place such vast accumulations of fossil 

 shells, fragments of so many Ammonites several feet in diameter, 

 or of gigantic stems of corals ; so much so, that perhaps there is 

 no other locality on the whole surface of the earth, where over 

 several square miles such an immense mass of organic remains 

 are dispersed. Some Ammonites are figured by Galeotti and de- 

 scribed by Nyst, but neither the description nor the figure gives 

 a clear view of the whole ; they remind us chiefly of the Ammo- 

 nites Carderoni of D'Orbigny. This same Trigonia again appears 

 in South America, in the mountains of S. Fe de Bogota, whence 

 they were first brought to us by Von Humboldt (Petref. recueillies 

 en Amerique, p. 8. f. 10). It occurs here dispersed over a wide 

 space, from Socorro on the north to Tocaymo on the south of Santa 

 Fe. It also shows the same depression of the lower border, the 

 same acute angle, scarcely exceeding 60°, of the anterior and pos- 

 terior margin, the same number of perpendicular plications on 

 the sides, and the same crenulations on the plications. It seems 

 therefore without sufficient foundation that some naturalists be- 

 lieve this Trigonia to be a new species. D'Orbigny has quoted it 

 with some doubt as Trigonia subcrenulata *, and Lea under the 

 name of Trigonia Tocaymaana f. Since now the mountains of 

 Santa Fe are proved most distinctly by the organic remains in- 

 closed in the strata to belong to the middle cretaceous series, as 

 I have endeavoured to prove in the description of Humboldt and 



* Coquilles de Colombie par M. Boussingault : Paris, 1842, p. 52. pi. 4. 



t Trans. Amer. Phil. Soc. 2nd ser. vol. vii. p. 6. pi. 9. f. 8. 

 Ann. $ Mag. N. Hist. Ser. 2. Vol. v. 25 



