Sharpe, Q. J. G. S. Quarterly Journal of the Geological Society of 



London, vols. v, vi, and xi. 

 Sharpe, Foss. Moll. Chalk. The fossil mollusca of the chalk of Great 



Britain. Palseontological Society of London, 1853. 

 Shuraard (B. F.) Marcy's Report, Explorations of the Red River 



of Louisiana. 1853. 



Id, Proceedings of the Academy Nat. Sci. Philadelphia. 

 Id. Transactions of the Academy of Arts and Sciences, St. Louis. 

 Sow. Min. Con. Sowerby (Jas.), The Mineral Conchology of Great 



Britain. London, 1812-1829. 



Sowerby (J. de C.) G. T. Trans. Geological Soc. London, vol. iv. 

 Tuomey. Proceedings of the Acad. Nat. Sci. Philadelphia, 1854. 

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After the references to the authors and place of publication are 

 placed those designating the localities. I have mentioned, when a 

 species occurs in America, the particular State or States in which it 

 is found. In all other cases I have only stated the country. The 

 following are the abbreviations used : 



Ala., Alabama, ' G., Germany, N. G., New Grenada, 



Ark., Arkansas, L, India, N. J., New Jersey, 



C., Chili, Mex., Mexico, N. M., New Mexico, 



Cr., Crimea, Miss., Mississippi, R., Russia, 



Del., Delaware, Mo., Missouri, Sw., Sweden, 



E., England, Neb., Nebraska, Tex., Texas. 

 Fr., France, 



The position in the formation is designated by the initials at the 

 right hand of the page, as follows : C., Chalk, U. G., Upper Green- 

 sand, G., Gault, L. G., Lower Greensand, N., Neocomien. 



The synonyms are placed under the generic heads in which they 

 were given, and the real names of the species are distinguished from 

 the synonymical ones as follows : 



EXOGYRA. 



costata, Say, &c. 



ponderosa, Roetn. (costata), &c. 



OSTREA. 



Americana, Desh. (ExoGYRA costata), &c. 

 Generic synonyms are designated thus, Exogyra. 



