34 COLEOPTERA OF NORTH AMERICA. 



is distinct or in front of tlie angle, wlien it is obtuse or rounded. 

 Elytra margined at base, sides narrowly inflexed, margin entire 

 without internal plica, apex obliquely sinuate, sometimes deeply, 

 , or even barely perceptibly, dorsal punctures usually present, rarely 

 (Pristonychus) wanting, surface striate, the eighth stria distant 

 from the margin, except in Perigona. Prosternum not prolonged 

 at tip. Mesosternal epiraera narrow. Metasternal epimera dis- 

 tinct, posterior coxae contiguous Legs slender, the femora some- 

 timesthickened, tibiae slender, not sulcate externally, the middle 

 and posterior slightly ciliate externally, the anterior slender, 

 eniarginate within, spurs moderate in length. Tarsi slender, the 

 joints often sulcate on tlieir'outer side, the fourth entire, eniargi- 

 nate or bilobed. Claws simple, finely serrate or pectinate. 



The males have the anterior tarsi with three joints feebly 

 dilated and squamulose beneath. 



Perigona seems also better placed here than elsewhere, and 

 appears to lead towards the Trechini in the same manner that 

 OUdhopus does to the Lebiini. 



A study of the form of the ligula and paraglossa of those 

 genera which are acknowledged on all sides to be undoubted 

 members of the present tribe Platijiius, Calathiis, and OUdho- 

 pus, seems to show what little value these organs have in the 

 definition of tribes and groups of genera. The ligula of Olis- 

 thopus is very plainly that of many Lebiides, Platynua reproduces 

 very closely that of Pterostichus, Calalhus proper is as nearly as 

 possible intermediate between the two, while the section Prido- 

 dactyla is a modification of Platynus. The tip of the ligula is 

 free in Platynus and Pridodactylu, and not free in the othergenera. 

 The mentum tooth also seems to furnish characters of an 

 evanescent nature. In some Platynus, especially those in which 

 the hind angles of the thorax are distinct {hrunveomarginatus, 

 ovipcnnis, etc.), the tooth is longitudinally impressed and eniar- 

 ginate at tip, while in the Agonuni type the tooth is very obtuse. 

 The same variation is observed in Calalhus, some having quite 

 an acute tOoth, others even bifid. 



The genera in our fauna are divisible, primarily, into two 

 groups by the following characters: — 



Eighth elytral stria distant from the margin and not deeply impressed ; 



thorax truncate or eniarginate at base. Platyni. 



Eighth elytral stria confluent with the margin in its basal half, deeply 



impressed and attaining the suture. PERiG0N.as. 



