112 COLEOPTERA OP NORTH AMERICA. 



clavate ; the labruni is distinct, and fits closely to the front, leav- 

 ing no epistoma. 



The species are found under stones ; on the Pacific coast none 

 have occurred south of Oregon. 



Mandibles concealed by presternum in repose, labrum visible ; 



Anterior tarsi retractile. Cytilus. 



All the tarsi retractile. Byrrhus. 



Mandibles, eyes, and labrum concealed in repose. Syncalypta. 



The species of the last genus have on the upper surface long, 

 clavate, upright bristles. 



Tribe III.— LIMNICHINI. 



Very small species, found on the margin of watercourses, where 

 they burrow in the ground, and emerge when the water is thrown 

 on the banks. A faint clypeal suture divides the front, but, owing 

 to the dense punctuation, is frequently scarcely visible ; the labrum 

 is distinct; the antennae, inserted at the sides of the front, are 

 only 10-jointed, and the three outer joints form a club, almost 

 solid in Physemus, feebly defined in Limnichus. The head is 

 strongly retracted in both genera ; the tarsi are free. 



Eyes, labrum, and mandibles concealed in repose. Limnichus. 



Eyes, labrum, and mandibles free ; club of antennae received in cavities at 

 the anterior angles of the thorax, on the upper surface. Physemus. 



The second genus is represented by a very small species from 

 the Colorado desert: the first by several species in the Atlantic 

 States. 



Sub-Family III.— CHELONARIIDAE. 



This sub-family is represented in our fauna by a single species 

 of Chelonarium (C. Lecontei Dej. Cat.), as yet undescribed, and 

 unknown to me. The tropical species are found on leaves of 

 plants. They are elongate, oval, moderately convex insects, with 

 the thorax strongly margined on the sides and front ; the head 

 retracted flatly upon the breast, leaving, however, the eyes, man- 

 dibles, and labrum visible; the antennas are inserted upon the 

 front, closely approximated, 11-jointed, filiform; epistoma not 

 separate from the front. Legs very contractile; tarsi with the 



