Page:Wood 1865 - The Myriapoda of North America.djvu/55

190 the base of the antennæ. The latter are generally short, thick, and clumsy, indeed in many genera they seem almost incapable of fulfilling any physiological function. The external organs of nutrition are arranged in accordance with two types or plans. The one is adapted for feeding upon decaying vegetable matter, the other for the imbibition of liquid or semi-liquid food. In each there is so much coalescing and atrophying of parts that it is impossible to trace in the adult their homologies. Iulus marginatus may be taken as an example of the first type. On examining the mouth of this myriapod, it will be found that the anterior or upper boundary is formed by the thin edge of the head; whilst the lower is the edge of a flat plate (Fig. 23), which forms the lower surface of the buccal cavity and throat. Working between this plate and the head are the jaws. Ihese are very massive, and appear to consist of three joints; the two proximal of these are firmly connected, almost coalescent, whilst the distal is united to them by a membranous suture. The basal or proximal part articulates with the head just beneath and posterior to the ocelli, and is so placed as to have its long axis nearly parallel with that of the body. Near to its distal extremity the mandibles curve abruptly at right angles, so that the distal joints (Fig. 24) present two opposing surfaces or edges. These are firm, hard, and more or less thin and acute. They are armed with more or less strongly pronounced conical elevations or teeth, lg and seem well adapted for breaking and cutting off substances.

The floor of the mouth and under surface of the head is formed by a single thin flat plate (Fig. 23) composed of several closely united pieces. The outer anterior part is formed on each side by a triangular piece, from which project a pair of short, blunt processes.

In the sugentia, or second division, the parts about the mouth are all consolidated into a tube-like projection or beak of greater or lesser length.

The American species of this suborder, which have come under the author's notice, are in this paper arranged in three families, the Iulidæ, Lysiopetalidæ, and Polydesmidæ. A fourth, the Polyxenidæ, is said to be represented. Of these, the first two constitute the Iulidæ of Newport, they themselves ranking as subfamilies in the classification of that authority. If any force is to be given to the characters employed by Mr. Gray, his