Peaiy, Robert E. Report of the Operations of the North Greenland Expedi- 

 tion of 1891-1892 342 



Pilsbry, H. A. New and unfigured Unionidj« (Plates VII and VIII) 131 



On the Anatomy of Sagda, Cysticopsis, yEgista and Dentellaria (Plate 



XJII) 213 



Notes on a Collection of Shells from the Stale of Tabasco, Mexico (Plate 



XIV) 338 



Preliminary Outline of a new Classification of the Helices 387 



Rand, Theodore D., William W. Jefferis and J. T. M. Cardeza, M. D. Min- 



eral Localities of Philadelphia and Vicinity 174 



Rhoads, Samuel N. The Birds of Southeastern Texas and Southern Arizona 



observed during May, June and July, 1891 98 



Ryder, John A. On the Mechanical Genesis of the Scales of Fishes 219 



The Principles of the Conservation of Energy in Biological Evolution : 

 a Reclamation and Critique 455 



Scott, W. B. A Revision of the North American Creodonta, with notes on 



some Genera which have been referred to that Group 291 



The Evolution of the Premolar Teeth in the Mammals 405 



Skinner, Henry, M. D., and Levi W. Mengel. Greenland Lepidoptera 156 



Stone, Witmer. Birds Collected by the West Greenland Expedition 145 



Walker, Ernest. The Autosporadic Seeds of Oxalis stricta 288 



Wistar, Isaac J. Remarks on the Quantity, Rate of Consumption and prob- ^ 

 able Duration of North American Coal, and the consequence to Air- 

 breathing Animals of its entire Consumption 82 



Wright, G. Frederick. Extra-Morainic Drift in the Susquehanna, Lehigh 



and Delaware Valleys 469 



