ARTICULATA. 113 
Fam. 6. Oniscide. These animals are either marine or terrestrial, the 
first pair of antenne are rudimentary, the second only being fully developed 
and conspicuous. The feet are slender, and formed for walking. The 
terrestrial genera (Porcellio, pl. 78, jig. 22) inhabit humid places, as cellars, 
crevices in walls, beneath stones or loose bark, and similar localities, feeding 
upon decaying vegetable matter. The female carries the eggs in a sac 
beneath the body. When the young first make their appearance, they have 
a segment of the body and a pair of feet fewer than the adult; and the head 
and antenne are proportionally larger. The young are retained for a short 
time between the respiratory lamin. Onzscus affinis, Say, is a common 
American species. 
The singular marine genera, Pycnogonwm and Vymphon (pl. 78, figs. 32, 
33), with but four pairs of legs, were formerly placed in this, or the preceding 
or succeeding order, by various authors, but they are by many believed to 
belong to the Arachnida. 
Orpver 7. Lamopreopa. The animals of this order are small, and present 
an unusual aspect. The head is small, the thorax has six segments, and the 
posterior extremity ends in a little tubercle corresponding to the abdomen. 
There are four antenne ; the-mouth has a pair of toothed mandibles, two 
pairs of lamellar maxille, and one pair of foot-jaws. There are five or 
seven pairs of feet, and in the former case the missing ones are generally 
those of the third and fourth pairs, which are represented by lamellar scales. 
The feet are prehensile, and the first and second pairs have a kind of hand 
capable of holding; the former are affixed to the head, and the latter to the 
thorax. Branchial vesicles are attached to the second or third thoracic 
segments, and sometimes to the first. The order contains two families. 
Fam. 1. Caprellide. Caprella (pl. 78, jig. 23) is a small and very 
slender animal with thin feet, a thick head narrowing posteriorly, and the 
first pair of antenne larger than the second. The species live among 
marine plants, along which they walk in the manner of a leech. In 
swimming, they bend the posterior extremity and straighten it suddenly. 
Fam. 2. Cyanide. Cyamus (pl. 78, fig. 24) is a genus found in colonies 
parasitic upon whales. 
Orver 8. Ampuipopa. This order takes its name from having two kinds 
of feet, cheliform and simple, and because the feet vary in the position of 
the former. The body is compressed, the back generally arched, the 
mandibles with a palpus, the eyes immovable, and the posterior extremity 
generally with styliform appendages, and turned beneath. The segment 
next the head supports the first pair of feet, which correspond to the second 
pair of foot-jaws. The antenne are slender and project in front. Most of 
these little animals swim with great vigor, by curving the tail beneath the 
body and jerking it back. There are fresh water as well as marine species, 
and they may be seen in most springs of fresh water. Some are found upon 
_ the beach under sea weed, or burrowing in the sand, and as they are too 
narrow to walk, they jerk themselves along whilst lying upon one side. 
There are two families, each of which contains several sub-families. 
Fam. 1. Gammaride. In most of these, the thorax is composed of 
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