Page:Wood 1865 - The Myriapoda of North America.djvu/78

Rh genus Polydesmus, as defined by H. De Saussure; but, not being entirely certain that my specimens are adults, I have refrained from indicating a new genus.

When surface markings exist on the scuta, they are very useful in defining species. The color is also a good character in some groups. Where one of these fails us the other very generally assists. The form of the last scutum is sometimes distinctive. The best characters, however, are those derived from the genital organs. The form, &c., of the antennæ and head often afford some clue.

POLYDESMUS, Latreille.

The head is broad, and has its anterior surface pubescent. The antennæ are rather long, filiform, pubescent, and strongly clavate. The first scutum is transversely oval. It is narrower than the head. The surface of the scuta is covered with minute flattened tubercles. On the more anterior these are quite distinct and arranged somewhat regularly in a fourfold series. On the more posterior they become less and less distinct, so that in some individuals these scuta have scarcely more than a rough appearance. Many of these tubercles are seta-tipped, and on the posterior borders of the scuta they become conical and acute, each with its rigid hair forming a sort of fringe. The lateral laminæ are broad and not widely separated. The serrations are less strongly pronounced on the