14 AMERICAN COLEOPTKRA. 



In many respects Amara is one of the most difficult genera of the 

 Carabidse. Altliough the members of certain of the subgenera are 

 easily recognizable as such, there are others the species of which 

 resemble each other very closely. Indeed, in those that are distin- 

 guished by differences in the secondary male characters, as, for inst- 

 ance, Aviara proper and Celia, there is often much diffiiculty in 

 determining to which subgenus a female should be referred when 

 unaccompanied by specimens of the opposite sex. In all the sub- 

 genera of whicii the species are numerous, there are several bearing 

 a close resemblance to each other, while in some, the extreme forms 

 of which are quite easily recognizable, the specific characters are 

 subject to variation and specimens occur which can only be doubt- 

 fully placed. This is especially the case in Cyrtonotvs, some species 

 of which, as laticollis, carinata and adstrieta, ai'e almost incapable 

 of definition. The genus as a whole is singularly devoid of those 

 minor characters such as dorsal punctures, differences in color and 

 markings, spots, elytral fovese, etc., which are often of great service 

 in the separation of closely allied species. As Dr. Horn says with 

 regard to Celia, species " can be properly studied by series of speci- 

 mens and not by uniques, except they be typically selected." 



It may perhaps be well to mention the more important structural 

 characters used in the classification of our species. 



The form of the mentum tooth has been used by Zimmermann, 

 and after him, by many authors as a primary character for the sub- 

 division of the genus. In a large majority of the species the tooth 

 is bifid or emarginate at tip, while in those referred to Amathitis 

 Zimm. and Acroclon Zimm. it is entire. Horn has observed a ten- 

 dency to variation in the depth of the emargiuation of some of our 

 species of Celia, and has regarded Acrodon as a group of species of 

 that subgenus. Putzeys has noted that the form of the acute tooth 

 is subject to variation in Amathitis, which is, however, not repre- 

 sented in our fauna. 



The antennaj are usually slender. In one species of C'yrtonotus 

 they are distinctly thickened. In certain species of Amara s. s. the 

 second and third joints are somewhat compressed and carinate; a 

 character of considerable importance. 



But little variation is to be seen in the palpi. In A. arenaria 

 Lee. the last joint is slightly swollen and acuminate at tip. 



The frontal grooves are short, sometimes almost punctiform and 

 often feebly impressed. .4. hamatopa Dej. (similis Kirby) is, how- 



