72 MEMOIRS ON THE COLEOPTERA 



As is well known, our territories west of the looth meridian are 

 very broken, and include many isolated mountain crests and valleys 

 having between them no direct communication. Within these 

 local environments primitive stocks become modified in the course 

 of time, and if the isolation has been sufficiently long continued 

 and the evolutionary stimuli potent enough, may result in forms 

 so distinct as to demand recognition as subspecies, species or even 

 genera, as in the case of the animals and plants now inhabiting the 

 islands off the coast of California. Reviewers of the Coleoptera 

 as a rule have not sufficiently considered these facts, generally 

 holding such heterogeneity in their material to be due simply to 

 fortuitous variation because of inherent plasticity, whereas in 

 reality true variation is a term properly applicable only to de- 

 partures from the mean among individuals inhabiting a common 

 environment. I find that this kind of inconstancy or instability 

 characterizes the species of Tenebrionidse but little more than it 

 does the Carabidae for instance,* for in all cases where it has been 

 possible to secure series of individuals taken together in the same 

 locality, no divergence sufficiently notable to give rise to doubt as 

 to specific status can be observed among the material serving as 

 the basis of this revision. Each species may have some particular 

 character which is especially variable, such as the longitudinal 

 extent of the reflexed elytral margin in the males of Asidopsis 

 cochisensis, for example, though the summation of features con- 

 stituting facies or habitus remains quite fixed. 



Having gradually accumulated my rather extensive material in 

 the Asidini from many collectors, each of whom has generally sent 

 but one or two examples from his series of any particular species, 

 it naturally results that a large proportion of the forms now making 

 up this material must be in uniques, so far as my collection is con- 

 cerned. This is of course the condition to greater or less degree 



* Individual instability in the Tenebrionidae is admittedly somewhat more obvious 

 than in such a family as the Carabidae, as indicated by the greater inconstancy of form, 

 as well as by the evidently greater tendency of the species to become modified by altered 

 environmental conditions. I have, for example, found Harpalus caliginosus repre- 

 sented by absolutely similar individuals on the Atlantic coast and in the mountains 

 of northern California. More recently evolved types of animals incline to plasticity 

 and instability to a greater degree than older and more established types, and this is 

 therefore an additional reason for considering the Tenebrionidae a comparatively 

 recent development in the Coleoptera, as stated further on by way of other reasoning. 



