NORTH AMERICAN COLEOPTERA. 307 



tnres, which are more distinct at the sides, the intervals distinctly punctate in 

 the scutellar region, but very indistinctly or smooth elsewhere. Body beneath 

 piceous. semi -opaque, metasternal area shining, sparsely punctate, mesosternal 

 area coarsely and closely f)unctate. Legs rufo-testaceous. Length .08 — .10 inch. ; 

 2 — 2.5 mm. 



The prosternum is carinate on the median line as in Cercyon. 



The pubescence of the surface is very fine, sparse and soft, in most 

 of the specimens not visible and at best rarely seen, except on the 

 sides of the elytra. 



In some partly immature specimens the elytra are slightly paler 

 at apex. 



Occurs in Arizona and Texas in decomposing Cactus stems. 



Group MEGASTERNI. 



The elytra clasp the body and are slightly inflexed beneath it, 

 there being no distinct lateral edge and the epipleurse .scarcely dis- 

 cernible. The side pieces of the metasternuni are partly covered by 

 the elytra so as to be much narrowed. The middle coxje are widely 

 separated, almost entirely by a large mesosternal area, which is pent- 

 agonal in two genera and oval in a third. Metasternum not or very 

 little prolonged between the coxfe and very closely united with the 

 metasternum the suture scarcely visible. Prosternum at middle ele- 

 vated to the plane of the mesosternum forming an ai-ea differing 

 in shape in the genera. First ventral segment carinate. 



The following genera occur in our fauna: 



Lateral margin of prothorax not inflexed. 



Anterior tibiae rather deeply excised on the outer edge near apex. 



Mescasteriium. 



Anterior tibipe entire ; elytra costate Peinelns. 



Lateral margin of prothorax angularly inflexed : antei-ior til)iie entire. 



Cryptopleiiruiii. 



Megasternum has not a sharply defined metasternal area, Crypto- 

 pleurum has the area extended by a well defined elevated line, while 

 Pemelus has an abruptly impressed area along the posterior margin. 

 The metasternal episternum is completely covered in front, wider 

 posteriorly in Cryptopleurum, wider in front and more covered pos- 

 teriorly in Megasternum, while in Pemelus it is narrowe.st at middle 

 and wider at each end. 



The species of these genera seem to be the furthest extreme of the 

 Hydrophilide type in both structui'e and habits. 



