CONTENTS 



OF 



VOLUME 1.— .PART II. 



Officers of the Academy of Natural Sciences for the year 



1818 Page 221 



Descriptions of several new species of North American Fishes. 



By C. A. Le Sueur 222 



An account of the Crustacea of the United States. By Tho- 

 mas Say (continued.) 235 



Observations on two species of the genus Gracula of Lathan». 



By George Ord 253 



Report of a committee on a new Hydrostatic Balance, in- 

 vented by Isaiah Lukens, and submitted to the Academy. 260 



Essay on the formation of Rocks, or an inquiry into the probable 

 origin of their present form and structure. By VViiliitm 

 Maclure. 261 



Account of two new genera, and several new species, of fresh 



water and land Shells. By Thomas Say. . . . 276 



Essay on the formation of Rocks, or an inquiry into the proba- 

 ble origin of their present form and structure, hy Wil- 

 liam Maclure (continued.) 285 



Observations on a new genus of Fossil Shells. By C. A. Le 



Sueur 310 



An account of the Crustacea of the United States. By Tiio- 



mas Say (continued.) . . . . , . 313 



Observations on the genus Glycine and some of its kindred 



genera. By Stephen Elliott 320 



Essay on the formation of Rocks, or an inquiry into the proba- 

 ble origin of their present form and structure. By Wil- 

 liam Maclure (concluded.) . . . . . 537 



An account of the Florida Jay of Bartram. By George Ord. 345 



Description of scveial species of North American Amphibia, 



accompanied with observations. By Jacob Green. . 348 



Descriptions of several new species of North American Fishes. 



By C. A. Le Sueur (coniinued.) .... 359 



