North American Species of Trogojohloeus. 325 



those given in the present paper which can properly be con- 

 sidered more than a mere rough diagnosis. If, for instance, in- 

 stead of saying **prothorax one-half wider than long, narrower 

 than the elytra, strongly rounded at the sides, narrowed toward 

 base, densely punctate," which is one of the usual forms of 

 orthodox diagnosis, and which might apply equally well to a 

 great many species of the same genus, we could give the actual 

 width at the widest part, the distance of this line from the apex 

 measured along the median line, the length of the latter, and 

 the width of base and apex, we should have something absolute 

 to guide us. The terms coarsely, finely, densely, sparsely, etc., 

 have no meaning except in a relative sense, and what, for in- 

 stance, in one genus or part of a genus, may be dense punctua- 

 tion, may in another be quite sparse. An absolute scale of 

 measurement would therefore prove of inestimable value in this 

 respect also. 



Another advantage of the proposed system should not pass 

 unnoticed, as it is of very great importance. On examining the 

 greatly magnified image of an insect, it will be apparent after 

 a little experience, that the mutual relationship of the larger 

 parts of the body, especially in regard to relative dimensions, is 

 not so easily grasped as in the very much reduced image of the 

 hand-lens. This should not be urged against the use of the 

 microscope, because it simply arises from the fact that the eye 

 is unable to consider, at the same instant, two widely separated 

 parts of the body in such a large image. If the system of actual 

 measurements be employed, however, this fault Would be entirely 

 overcome, and the only objection which can reasonably be urged 

 against the use of the microscope would be forever set at rest.* 



* The objection urged by several entomologists, that the greatly en- 

 larged images given by the microscope bring so much detail into view as 

 to cause undue weight to be given certain characters which may be in- 

 dividual rather than specific, is scarcely worthy of consideration. That 

 it is true of the novice who has not yet learned to interpret what he 

 sees, none can speak with more feeling than the author himself, who, 

 in his earlier inexperience, was led into several very regrettable errors, 

 and notably in the case of Harpalus viridiceneus, wherein he over- 

 estimated the importance, of the role played by certain adventitious 

 setae; but to say that, in a mature judgment, the mere fact that every 



