LARVA OF PLATYPSYLLUS CASTORIS—DORSAL VIEW.
PLATYPSYLLUS CASTORIS.
Where the characters of the image have been so often described, it is unnecessary to refer to them in detail, and I will only call attention to the more striking structural features and to some omissions by, or differences between, previous authors. A glance at the illustrations which I have prepared will show the prevailing characteristics of this interesting creature, its general
ovoid and flattened form, and more particularly the flattened semicircular head. Dorsally, we notice the rather prominent occiput fringed behind with short and broad depressed spines or teeth which form a sort of comb, the prothorax trapezoidal and but very slightly curved, with side margins strongly grooved. There is a very distinct scutellem, and the two elytra are rounded at the tip and without venation. Hind wings and eyes are both wanting. The abdomen shows five segments, each with a row of depressed bristles.
On the ventral surface we find among the more curious characteristics, first the antennæ; these were originally described by Westwood as three-jointed, the club being annulated. Le Conte could not distinctly make out the number of annular joints upon this club, though he thought he detected seven, which made nine joints to the whole antenna. The club is received in the deep cup-shaped excavation of the second joint. Horn thought he detected a division of the second joint, and resolved but six segments in the club, making also nine joints to the whole antenna, but in a somewhat different fashion from Le Conte. Westwood's figure shows eight annuli to the club. He failed to find any trace of the mandibles, but Le Conte described them as small, flat, subquadrate, with the inner side deeply crenulate, and resembling those of Corylophus; the stipes well developed, and biarticulate. Horn could not entirely make out the mandibles as described by Le Conte, and rather concluded that what Le Conte described is really one of the granules which occur behind the labrum. He considered that the piece could hardly be even an aborted mandible, because of its diminutive size.
YOUNG LARVA.
What all authors have agreed in calling the mentum is very noticeable, being large and broad, and trilobed behind. The maxillæ are strong, with complicated stipes and with two flat, thin lobes, the inner one smaller than the outer and rounded at the tip, both lobes being ciliate. The maxillary palpi are four-jointed, the labial palpi three-jointed. The prosternum is very large, subtriangular, concealing the insertion of the coxæ, and extending over the front part of the mesosternum, as does this over the front of the metasternum. Six ventral segments of the abdomen are visible behind the posterior coxæ, which conceal two and the base of a third. The coxæ are flat and not at all prominent. The legs are characterized by broad and flattened tibiæ and femora, and the strong spines with which they are armed. The tarsi are five-jointed, the front and middle pair with a row of claviform membraneous appendages each side, which Le Conte found only in the male.
American entomologists have been satisfied to follow Le Conte and Horn as to the position of Platypsyllus. Yet with such diversity of opinion on the subject among high European authorities, the importance of a knowledge of the adolescent states has been recognized, as the character of either the larva or pupa would settle the question.