PREFACE. 



The following Memoir was commenced seven years ago, and, although various 

 circumstances have interfered with its completion until now, the delay has not 

 been unattended with some advantages. During the lapse of time nearly as much 

 new material has been discovered as was originally at the command of the author, 

 and thus our acquaintance has been greatly extended with the subjects of the 

 memoir. In consequence the latter has been repeatedly altered, and portions have 

 been intercalated, which may serve to explain any apparent want of continuity in 

 the work. 



The author takes the opportunity of acknowledging his obligations to Prof 

 George H. Cook, of Rutgers College, New Brunswick, New Jersey, who has 

 given constant and important aid in procuring specimens for examination dur- 

 ing his geological explorations of the State. Acknowledgments are also due 

 to W. Parker Foulke, of Philadelphia, through whose especial exertions we 

 are indebted for the discovery of the huge Reptile, Hadrosaurus, which forms 

 one of the most interesting and important subjects of description in the suc- 

 ceeding pages. Valuable assistance has also been rendered by others in ob- 

 taining specimens for investigation, but more especially by Dr. J. H. Slack, of 

 Philadelphia. The basis of the work has been mainly founded on the rich collec- 

 tion of the Academy of Natural Sciences of Philadelphia. 



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