1891.] NEW YORK ACADEMY OF SCIENCES. 81 



able habitats — although known to run into something else; or was 

 there a still better way of expressing such important biologic 

 facts ? Here were evidently recognizable stages in the process of 

 erolution by environment. How were they to be recognized so as 

 to be made use of in philosophical biology ; in what way could 

 they be chronicled in descriptive biology ? That many of these 

 intergrading forms possessed noteworthy differences is evident 

 from the fact that they formerly held the rank of unquestioned 

 species. 



For a time a wavering course was followed, some writers lump- 

 ing as one species all forms that seemed to intergrade, while 

 others continued to recognize all of the more prominent phases 

 as species. Soon after it became the fashion to distinguish them 

 as varieties, under what may be termed a qualified quadrinomial 

 system of nomenclature. Thus our Eastern red squirrel, or 

 chickaree, was called Scinriis liudsonius; its Kocky Mountain 

 representative, or Fremont's chickaree, became Sciurus huclso- 

 nius, vai". fremonti; another Rocky Mountain form, known as 

 Richardson's chickaree, became Sciurns hudsonius, var. rich- 

 ardsoni; a Northwest coast form, known as Douglass' chickaree, 

 became Sciurus Jiudsoniua, var. douglassi ; and so on in all sim- 

 ilar cases. This proved a cumbersome method, and soon the 

 term ''var." was dropped, resulting in a trinomial name, ^Dure 

 and simple, for the designation of subspecies. This in reality is 

 the binomial system of Linne in spirit, modified slightly in the- 

 letter to fit what was an ideal system of nomenclature at the 

 time of its inception, to the requirements of modern biology. 

 Hence American mammalogists adojited, in common with orni- 

 thologists, trinomial designations for nascent species, reserving 

 the binomial distinctively for species in full standing. This 

 system became generally current about 1883. 



The several geographic, intergrading forms of a wide-rang- 

 ing species often differ more from each other in their extreme 

 phases than do, in other cases, perfectly distinct species. Hence, 

 through the use of trinomials, two important things are accom- 

 plished: first, a means of distinguishing two kinds of relation- 

 ship among congeneric forms, the use of a binomial name in- 

 dicating entire distinctness, without regard to kind or degree 

 of difference, Avhile tlie use of a trinomial implies known in- 

 tergradation, notwithstanding the very wide difference which 

 frequently exists between the extreme phases of a group of inter- 

 grading or conspecific forms ; secondly, provision for a conve- 

 nient and tangible way of giving expression, by means of a definite 

 formula, to some of the most suggestive facts in the evolution 

 of life. It is not claimed that this is a perfect system of nomen- 



