Sub-Fam. 3. Obisiinae.—The cephalothorax of the Obisiinae does not narrow—and is, indeed, sometimes broadest—anteriorly. The chelicerae are notably large, and the dorsal abdominal plates undivided. They are the most active of the Chernetidea, ordinarily running backwards or sideways with their pedipalpi closely folded up against the body. Four genera usually admitted fall within this group:—Obisium, Roncus, Blothrus, and Chthonius.
Obisium has four eyes, parallel-sided cephalothorax, and curved chelae on the palps. Roncus is like Obisium except in having only two eyes, and is therefore disallowed by Simon, who also considers Blothrus to comprise merely eyeless species of Obisium. In Chthonius the cephalothorax is broadest in front, and the digits of the chelae are straight.
The Obisiinae are found in moss and débris, and under stones. Three species of Obisium, two of Roncus, and four of Chthonius are recorded in England.
The subjoined list of British species of Chernetidea is taken from the monograph of the Rev. O. P. Cambridge, cited above:—
Group I.—Four eyes.
Chthonius orthodactylus, Leach.
„ rayi, L. Koch.
„ tetrachelatus, Preyssler.
„ tenuis, L. Koch.
Obisium muscorum, Leach.