168 GEO. H. HORN, M. D. 



Synopsis of the species of CITCHRUS inhabiting Boreal 



America. 



BY GEORGE H. HORN, M. D. 



The generic name Cychrus in the title is used in a general way to 

 include all the species described from time to time under the names 

 Sjjhseroderus and Sca2:ihinotus as well as Cj/chrus. 



The generic characters of these have been so often made known 

 in the books that it seems hardly necessary to repeat them in detail. 

 I will therefore mention those which may be necessary to illustrate the 

 meaning of various expressions made use of in the following pages. 



The head is elongate, more or less constricted behind the eyes 

 although at times hardly perceptibly, the eyes are more or less promi- 

 nent and distant from the apical margin of the thorax except in 

 Sphseroderns and C. elevatus. 



The antennae are slender and vary in length from a half to three- 

 fourths the length of the body, the basal joint in several species be- 

 comes enlarged and stout in proportion to the other joints. 



The genal margin of the head, that is the portion of the head 

 which encloses the buccal cavity at the side and directly behind the 

 base of the mandibles, shows some points of variation which are more 

 than specific in their nature. In the iScaphinotus group alone this 

 portion of the head is very feebly expanded, and as the base of the 

 maxillae is the portion immediately beneath this plate, when the latter 

 is feebly developed the maxillae become visible Irom above. 



The parts of the mouth do not exhibit any striking differences. 

 In angusticoUls the inner lobe of the maxillae is furnished on the 

 inner side with a row of moderately long, stout bristles, while in all 

 the other species there are merely hairs or pubescence. 



The sexual characters are of the greatest importance in the arrange- 

 ment of the species. 



In those species grouped below under the name Cychrus, the an- 

 terior tarsi exhibit no sexual characters whatever, they are neither 

 more dilated nor otherwise pubescent in the male than in the female. 

 In Sphseroderns on the other hand, the anterior tarsi of the male are 

 broadly dilated and densely spongy pubescent beneath. In the other 

 divisions, Pemplms, Brennus and Scaphinotus, the anterior tarsi are 

 moderately dilated in the male and may be either spongy pubescent 



