NORTH AMERICAN COLEOPTERA. 281 



Dr. Sharp has observed that in one genus, Cyloma, the first joint 

 of the middle and posterior tarsi is shorter than the second, while in 

 Perochthes the first joint is lost entirely. The shoitening and final 

 loss of the first joint of the tarsus in a tribe in which that joint 

 normally tends to be longer than the second is certainly very curious, 

 and suggests the thought of relationship in other directions than the 

 present tribe. 



For the better study of the species, and as a means of showing the 

 relationship between the genera, it is proposed to divide the tribe in 

 three groups in the following manner : 



Elytra extended below the lower surface of body, epipleurje in great part ver- 

 tical ; metasterual side pieces wide Group CYCLONOTI. 



Elytra not extended. 



Elytra not iuflexed, epipleurse horizontal, distinct; nietasternal side ]iieces 

 moderate in width, parallel ; prosternum carinate at middle. 



Group CERCYONES. 

 Elytra inflexed, clasping the sides of body, without distinct epipleurte ; nieta- 

 sternal side pieces narrow, partly covered by the inflexed elytra; jiroster- 

 num elevated at middle, forming an area Group MEGASTERNI. 



Group CYCLONOTI. 



In this group the metasternum is prolonged between the middle 

 coxse, closely united with the mesosternal elevation, the suture always 

 distinct, and often impressed. 



The following genera occur in our fauna: 



Prosternum moderately wide in front of the coxse and strongly carinate between 

 them ; elytra with distinct striae of punctures and an impressed sutural 

 stria; metasterual side pieces rather wide and with parallel sides; first 

 ventral segment carinate Dactylosteriiuui. 



Prosternum extremely narrow in front of the coxse and not carinate Ijetween 

 them ; elytra with confused punctuation and a well marked sutural stria- 

 metasterual side pieces moderately wide, the suture slightly arcuate; first 

 ventral segment carinate Pllteuotypus. 



Prosternum short in front of the coxse and not carinate between them ; elytra 

 with confused punctuation and no sutural stria ; metasternal area very 

 small; metasterual side pieces wide, widest at middle, the suture rather 

 strongly arcuate; first ventral segment not carinate.... Phieuonotuiii. 



In addition to the characters given above it will be observed that 

 the antennal club of Phfenonotum is quite loosely articulated, that 

 of Dactylosternum rather close, while in Phsenotypus that member 

 is quite compact. 



Other genera have been suggested which .should probably be re- 

 ferred to this group, viz., Cyclonotum Er., Cyloma, Perochthes and 



TRANS. AM. ENT. SOC. XVII. (36) SEPTEMBER, 1890. 



