SCARAB^EIDAE. 131 



Tribe IX.— TROGItfl. 



Mandibles and labrum corneous, prominent ; antennae 9- or 

 10-jointed, club 3-jointed ; anterior coxae rounded, subcorneal, 

 prominent; middle coxae nearly round, not oblique, contiguous; 

 epimera of the metathorax covered; epimera of the mesothorax 

 widely separated from the coxae by the sternum ; ventral segments 

 five, not connate ; abdomen covered by the elytra ; tarsi with 

 moderate claws, but no onychium. 



The insects of this tribe are oblong, convex species, living in 

 dried decomposing animal matter. The feet are scarcely fossorial 

 in form; the surface is usually rough, and covered with a crust 

 of dirt, removed with great difficulty. Our species are numerous, 

 and belong to the genus Trox. The larger species, having the 

 sides of the thorax not ciliate with hairs, were placed by Erichson 

 as a separate genus, Omorgus ; but the characters, as observed by 

 Lacordaire, are indefinite, and it is not retained.* 



The genus Trox possesses a distinct stridulating organ; it is 

 an elliptical plate, with pearly reflections, occupying the upper 

 part of the external face of the ascending portion of the first ven- 

 tral segment, and is covered by the elytra; on the inner surface 

 of the elytra, near the margin, about opposite the metathorax, is 

 an oval, smooth, polished space, which has probably some con- 

 nection with the stridulating organ. 



Sub-Family II.— MELOLONTHIDAE. 



This sub-family holds an intermediate position between the lapa- 

 rosticti and pleurosticti. The second pair of abdominal spiracles 

 is placed in the membrane connecting the ventral and dorsal seg- 

 ments, as in other Scarabaeidae ; in most species the third, and 

 sometimes the fourth, at the outer limit of this membrane ; the fifth 

 and sixth pairs are in the dorsal portion of the ventral segments, 

 but the lines connecting them do not diverge strongly, as in the 

 pleurosticti; the seventh or last pair is usually visible behind the 

 elytra, but variable in position ; in other species, forming the first 

 two tribes, however, the spiracles are placed as in the laparosticti, 

 all being in the connecting membrane. 



* For a synopsis of our species, see Proc. Acad. Nat. Sci., VII, 211. 



