BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 33, PP. 599-604 SEPTEMBER 30, 1922 



VARIATIONS OR SPECIFIC DISTINCTIONS: WHICH? 1 



BY RICHARD SWANN LULL 



{Read before the Paleontological Society December 30, 1921) 



CONTENTS 



Page 

 Introduction 599 



Age distinctions 600 



Sex distinctions 600 



Ontogenetic variations 601 



Introduction 



In the search for criteria for specific diagnosis, especially in fossil 

 mammals, too little heed seems to be given by the average systematist to 

 a number of aspects of individual variation which are manifestly such hi 

 living forms. As a consequence, our paleontologic literature is burdened 

 with a vexatious synonymy which requires extensive monographic study 

 to unravel. Too often the description is based on excessively fragmentary 

 material, whereas for enduring work not only should the type be as ade- 

 quately represented in all of its essential parts as possible, but as large a 

 series of individuals as may be had should be used with the idea of detect- 

 ing such characters as are merely individual and such as are truly diag- 

 nostic of the species. 



Among recent forms, three directions of variation are easily recog- 

 nized — those due to age, to sex, and to environment — under the last of 

 which comes the direct influence of climate, mainly the degree of mois- 

 ture, to a less extent of temperature, of altitude, and of peculiarity in 

 life conditions and consequent habits, with physical as well as physiolog- 

 ical reaction. Of course, the environmental variations may give rise to 

 what are called geographical variants, which are established in the 

 heredity, and as such may be incipient species, or the modifications may 

 be individual or ontogenetic only, to disappear as soon as the conditions 

 which gave rise to them change. 



1 Manuscript received by the Secretary of the Society March 28, 1922. 



(599) 



