448 COLEOPTERA OF NORTH AMERICA. 



First ventral suture arcuate ; 



Cotyloid surface of hind tibiae glabrous ; eyes without orbital groove ; 

 Hind coxal cavities open externally ; first abdominal segment behind 

 them very short. Mylacus. 



Hind coxal cavities closed externally ; first abdominal segment normal ; 

 Scrobes superior and convergent above ; 



Rostrum longer than the head, scrobes very short terminal ; body 



with scales and setie. Thricolepis. 



Rostrum short ; scrobes nearly attaining the eyes ; body scaly 



only. Peritelopsis. 



Scrobes more lateral, not converging above ; 



Scape as long (or very nearly so) as the funicle ; tibia? finely den- 

 ticulate witiiin. Geoderces. 

 Scape much shorter tlian the funicle ; tibiae not denticulate. 



Aragnomus. 



Cotyloid surface of hind tibiae densely scaly ; 



Scrobes superior, slightly convergent above ; 



Eyes indistinctly surrounded by a groove ; scape feebly arcuate. 



Dysticheus. 

 Scrobes lateral, not at all convergent ; orbital groove deep ; 



Scape arcuate and. slightly twisted ; scrobes lateral, deep, and at- 

 taining the eyes. Eucyllus. 

 Scape straight or very feebly arcuate ; 



Scrobes very shallow posteriorly, not attaining the eyes, 



Thinoxenus. 

 Scrobes deep, attaining the eyes. Rhypodes. 



The genera above indicated are so arranged as to exhibit a 

 gradual transition from the Ptoclioid forms of the preceding group 

 to the Trachyphloeoid forms of the next. The rostrum tends to 

 become shorter, also, as the advance is made from the first to the 

 last genus. The vestiture varies. In one species, Mi/lacus fiuc- 

 vatiis Lee, the surface is sparsely pubescent without scales, Pei'i- 

 telopsis globiventris Lee. is scaly only without trace of hairs or 

 setae; all the remaining species are densely scaly and with short 

 erect set^B. As a general rule the metasternal side pieces are 

 extremely narrow in the earlier genera (entirely concealed poste- 

 riorly in Mylacus) and become more distinctly wider in the later 

 genera, the suture, however, is so very indistinct as to make it 

 almost impossible to use the character systematically. 



The scrobes vary greatly in form, hi several genera they are 

 plainly superior and rather short, converging above. In others 

 it is not easy to determine whether to call them lateral or supe- 

 rior. When the scrobes are much more distinctly open when 

 viewed 'from above than when seen from the sides, thev are called 



