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 coxæ cylindrical, prominent; hind coxæ very small, contiguous, quadrate; tibiæ without spurs; tarsi without claws, joints each with a membranous 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 more 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 Hymenopteron 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 pupa 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.

Antennæ with six joints.

Antennæ with four joints.

STYLOPS.

XENOS.

Stylops inhabits bees of the genus Andræna; 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 collecting the species of this family.