Fig. 248.—The lesser death-watch of Upminster. (After Derham.) A, magnified; B, natural size.
Fig. 249.—Sphaeropsocus kunowii. From amber. × 30. (After Hagen.)
Numerous species of Psocidae are preserved in amber; Hagen[[319]] has made a careful study, based on a considerable number of specimens, of about thirteen such species. They belong to no less than nine genera and five sub-families. Sphaeropsocus is the most remarkable; this Insect has a well-developed prothorax, as is the case in the wingless Psocids, and a pair of large wings or tegmina meeting by a straight suture along the back, as is usual in beetles, though quite unknown in existing Psocidae. Another species, Amphientomum paradoxum, has the body and appendages covered with scales like a butterfly or moth; other species, found in gum-copal or still living, have scales on various parts of the body, but not to so great an extent as this amber species. The genus Amphientomum is still represented in Ceylon and elsewhere by living forms; Packard has figured some of the scales;[[320]] they appear to be extremely similar to those of Lepidoptera or Thysanura. The facts connected with this fauna of amber Psocidae would seem to show that the family was formerly more extensive and important than it is at present; we should therefore expect to find numerous fossil forms in strata of date anterior to that of the amber; but this is not the case, all that is known as to fossil Psocidae being that Scudder has recently ascribed traces of an Insect found in the Tertiary rocks of Utah to this family as a distinct genus.
Fam. V. Perlidae.
Insects of moderate or large size, furnished with four membranous wings; these are usually complexly reticulate; the hind pair are much the larger, and have a large anal area of more simple venation, which becomes plicate when folded. The coxae are small, the legs widely separated. The larvae are aquatic in habits; the metamorphosis is slight.
Fig. 250.—Pteronarcys frigida, male. (After Gerstaecker.)
The Perlidae form a small family of Insects unattractive in their general appearance. The life-history of each individual consists of two abruptly contrasted portions; the earlier stage being entirely aquatic, the later aerial. Hence the Perlidae come into the amphibious division of Neuroptera. The definition we have given above would, except as regards the texture of the front wings and the aquatic habits of the larvae, apply to many Insects of the Order Orthoptera. The Phryganeidae, another family of Neuroptera, have aquatic larvae and wings somewhat similar in form to those of the Perlidae, but the members of the two families cannot be confounded, as the Phryganeidae have hairy front wings and large and contiguous coxae.