278 COLEOPTERA OF NORTH AMERICA. 



Metathorax very large, greater in bulk than the rest of 

 the body, with the sutures of the dorsal pieces all distinct ; 

 the postscutellum is conical and prolonged far over the base 

 of the abdomen; wings very large, fan-shaped, with a few 

 diverging nervures ; the epimera are very large, and project 

 behind almost as far as the postscutellum. 



Abdomen small, with from seven to nine segments. 



Legs short; anterior and middle coxee cylindrical, promi- 

 nent; hind coxse very small, contiguous, quadrate; tibiae 

 without spurs; tarsi without claws, joints each with a mem- 

 branous lobe beneath. 



Females larviform, always contained in the pupa case. 



This family contains a small number of species which, by the 

 degradation of structure have lost all resemblance to the other 

 members of the order Coleoptera. They were, from the period 

 of their discovery to within a few years, considered as a separate 

 order, under the name Strepsiptera, but a knowledge of the 

 transformations, and a moi'e rigid interpretation of the external 

 anatomy has convinced nearly all systematists of the propriety of 

 placing them a family of Coleoptera. 



They are parasitic in the bodies of species belonging to various 

 genera of aculeate Hymenoptera ; the comparatively large size 

 of these parasites causes a distortion of the abdomen of the Hy- 

 menopteron affected, and, on close observation, the heads of the 

 pupa cases may be seen emerging between the segments. The 

 head of the pupa case of the male is convex, that of the female is 

 flat ; specimens containing male pupae can be kept confined with 

 proper food until the parasite is hatched. 



But two genera are yet known in North America, in both of 

 which the tarsi are 4-jointed. 



Antennae with six joints. Stylops. 



Antennae with four joints. Xenos. 



Stylops inhabits bees of the genus Androena ; I have never 

 met with specimens. Xenos Peckii lives in our common wasp 

 Polistes fuscata. I have seen stylopized individuals of Odynerus 

 quadricornis, and of a large species of Splex. 



It is very desirable that observers in the United States should 

 turn their attention to the laborious but interesting task of col- 

 lecting the species of this family. 



