COLE OP TER A. 
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spine as in Hydrophilus and Tropisternus , and the sternum 
of the prothorax bears a keel-shaped projection. Our most 
common species is Hydrocharis obtusatus (H. ob-tu-sa^us); 
this measures about five eighths of an inch in length. 
Some of the smaller species of this family are not aquatic, 
but live in moist earth and in the dung of cattle, where, it 
is said, they feed on dipterous larvae. 
Family PLATYPSYLLlD^E (Plat-y-psyl'i-dae). 
The Beaver-parasite . 
Only a single representative of this family is known ; 
this is Platypsylla cast oris (Plat-y-psyl'la cas'to-ris), which 
lives parasitically on the beaver. This beetle is about one 
tenth of an inch in length ; the body is ovate, elongate, and 
much flattened ; the wing-covers are short, about as long as 
the prothorax, and leave five abdominal segments exposed; 
the eyes and wings are wanting. 
Specimens of this remarkable insect are most easily 
obtained by beating over a sheet of paper the dried skins of 
beavers, which can be found at fur-stores. 
The family LEPTINIDiE (Lep-tin'i-daej is represented by 
only two species in North America. One of these is from 
the Hudson Bay region ; the other, Leptinus testaceus (Lep- 
ti'nus tes ta'ce-us) lives with various small rodents and inseo 
tivora, either on their bodies or in the material of their nests. 
It can be distinguished by the characters given in the table 
of families. 
Family SlLPPIID,E (Sil'phi-dae). 
The Carrion-beetles . 
The carrion-beetles are mostly of medium or large size, 
many species attaining the length of one and one half inches, 
while the smaller species of the more typical genera are 
nearly half an inch in length; some members of the family, 
however, are minute. The segments near the tip of the an.- 
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