PROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VIII, pp. 91-106 pls. iv-v July 10, 1906 



EVIDENCE BEARING ON TOOTH-CUSP 

 DEVELOPMENT. 1 



By James Williams Gidley, 

 Department of Geology, U. S. National Museum. 



In connection with the work of cataloguing the portion of the 

 Marsh collection of Mesozoic mammals, obtained under the au- 

 spices of the U. S. Geological Survey and now deposited in the 

 United States National Museum, I have made some discoveries 

 of seeming importance in the form of evidence bearing on the 

 question of tooth-cusp homologies in the mammalian molars. 

 This evidence I wish briefly to present in the following pages, 

 hoping it may throw some added light on the very important 

 subject of tooth morphology. 



Before proceeding, I wish to express my indebtedness to Dr. 

 George P. Merrill for making possible the arrangements for 

 this detailed study of material and for his encouragement in the 

 work ; to Prof. Charles Schuchert, of Yale University, for 

 submitting to my hand the type material of the Marsh collection 

 at New Haven ; and to Prof. Henry F. Osborn of the American 

 Museum of Natural History, for his courtesy in placing the 

 collection of Mesozoic mammals in that institution at my disposal. 

 My thanks are also due Mr. G. S. Miller, Jr., for his valuable 

 aid in selecting study material from the collection of modern 

 mammals in the National Museum and for a clear translation 

 of Herluf Winge's paper on tooth-cusp development. 



1 Based on a study of the Mesozoic Mammal Collection in the U. S. National 

 Museum. 



Proc. Wash. Acad. Sci., July, 1906. 91 



