well adapted for active service. The second scutum is never produced forwards at the sides so as to abut against the head, as in Spirobolus. In all the species in which I have had an opportunity of examining sexes, the form of the first scutum distinguishes them with certainty. In the male its antero-posterior diameter is large, and there are well-marked lateral margins running nearly at right angles to the others. In the female the anterior posterior diameter is much less, but laterally the scutum is so produced that the anterior and posterior margins may in most cases be said to meet one another at an angle. The males are further distinguished by a peculiar alteration of the first pair of feet, which are transformed into a pair of very large, thick organs. The function of these is obscure, but possibly it may be connected with the union of the sexes, analogous to that of the "claspus" in some reptiles.
I. impressus.
I. rubro-castaneus, linca dorsale nigra et maculæ nigræ seriebus lateralibus (interdum obsoletis) ornatus; antennis longis, filiformibus, pilosis, baud clavatis; scutorum lateribus canaliculars; segmentis 52; mucrone parvo.
Reddish chestnut, ornamented with a black dorsal line, and a lateral series of black dots (sometimes obsolete); antennæ long, filiform, pilose, not clavate; sides of the scuta canaliculate; segments 52; mucro small.
I. impressus, Say, Journ. A. N. S , 1st series, vol. ii, p. 102.
I. venustus, Wood, Proc. Acad. Nat. ScL, 1804, p. 10.
The general color of this species is reddish chestnut; frequently the red predominates so much that the individual is really flesh-colored, but occasionally the chestnut overcomes the other tint. The dorsal stripe is generally very distinct, especially on the posterior portion of the scuta. The eyes are triangular, and are connected by a dark band, which is often rather obscure. The anterior cephalic aspect is long and narrow, with its sides converging inferiorly. Its inferior border is fringed with a double row of short, distant hairs, and is medianly deeply emarginate, and 2—4 dentate. The scuta are ornamented, rarely with a white blotch on each side of the mesial line, but generally with two lateral black dots. The first scutum in the female has the anterior margin oblique as to the main axis of the body, and is prolonged laterally so as to form processes, mostly canaliculate, with a rounded border. In the male the anterior margin is at right angles to the axis of the body, and the lateral parallel to it, so that there are no processes. The male appendages consist of two main portions on each side. The outer and more conspicuous of these (Figs. 27, 28) is formed of a thin, very irregular plate, from whose base springs a short, clavate, cylindrical, distally pilose process. The inner portion (Fig. 26) is composed
