The Dysderidae are divided into two sub-families, Dysderinae and Segestriinae, for the most part confined to temperate regions.
(i.) The Dysderinae are easily recognised by a peculiarity of the sternum. Instead of being merely excavated along its border for the reception of the legs, its edge is folded round the coxae to meet the carapace, and thus forms a series of collars or sockets in which the limbs are articulated in perfect isolation from each other. These spiders vary considerably in size, and are generally of a somewhat uniform coloration, never marked with vivid patterns. There are eight genera of this sub-family, two of which are represented in England.
Dysdera cambridgii is not a rare spider under stones in rocky localities, such as the Isle of Portland, and occurs, though less commonly, all over the country in similar situations, and under the loose bark of trees. It is half an inch in length, with a chestnut-coloured cephalothorax and legs, and dull yellow abdomen. A closely allied species, D. crocota, also occurs more rarely.
Harpactes hombergii is common in vegetable débris and under decaying bark. It is about a quarter of an inch in length, of slender form, with black-brown cephalothorax and clay-coloured abdomen. The legs are yellowish and annulated. More than forty exotic species of Dysdera and twenty-four of Harpactes have been described. Another genus of the Dysderinae is Stalita, which comprises three species, inhabiting the caves of Dalmatia and Carniola.
(ii.) The Segestriinae include two genera, Segestria and Ariadna.
Segestria senoculata occurs in England in similar localities to those where Dysdera cambridgii is found. It is not much smaller than that spider, and has a dark brown cephalothorax and legs and a dull yellow abdomen, with a series of adder-like diamond-shaped black markings along the middle. Two other species have occurred on rare occasions in England, and twelve more are recorded from the various temperate regions of the world.
Ariadna is the only Dysderid genus which invades the tropical regions. It includes about twenty species.
Fam. 12. Caponiidae.—This is a small family of three genera and about twelve species, remarkable in having no pulmonary sacs but five tracheal stigmata,[[312]] and in the peculiar arrangement of their six spinnerets, those which are ordinarily median being in the same transverse line with the anterior ones.
The single species of Caponia (C. natalensis) inhabits South Africa, while Caponina has two species in South America. These spiders are eight-eyed, but the two median posterior eyes are much the largest, and these alone are present in the remarkable genus Nops, of which several species inhabit South America and adjacent islands.
Fam. 13. Prodidomidae.—This small family includes about twenty species of minute spiders from sub-tropical regions. They are eight-eyed, with short smooth legs, terminated by two claws not dentated. The spinnerets are especially characteristic.