462 ONISCID@. 
ISOPODA. ONISCID. 
NORMALIA. 
Genus—PLATYARTHRUS. (Brandt.) 
Generic character. Flattened, broadly ovate, scabrous. 
Cephalon transverse. Lateral and frontal lobes strongly 
developed, arising from the anterior margin. Outer antenne 
apparently six-jointed ; second joint small; third short, nar- 
rowed outwardly at its base; fourth, ovate; fifth, largest, 
broad, flattened outwardly, but narrowed at its base; sixth, 
thin, pointed at the tip, with a slight indication of a joint at 
its base. Terminal feet with the basal portion large, exposed. 
Terminal portion as long as the basal, conical. Inner appen- 
dage slender, exserted. 
THE type of this genus is closely allied to Oniscus 
and Porcellio, but differs in its short flattened antenne, 
scabrous, perfectly opaque, white body, as well as in 
various minor structural details. The head has its 
anterior lobes arranged nearly as in Armadillo, being 
derived, according to Dr. Kinahan, from the cephalic, 
mandibular, or fourth ring of the head, and not from 
the third or second, i.e., the antennary rings. The third 
is but badly developed and small, but the distinction 
between it and the fourth ring is evident. 
The internal antenne are three-jointed and very 
minute; the outer antennz are short but broad, flat, 
and scabrous, the fifth joint being much the largest, 
and dilated. We have not been able, with a powerful 
lens, to discover any articulation at the base of the ter- 
minal joint, as described by Dr. Kinahan, although a 
slight dilatation in the lateral margin near the base seems 
