50 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. xxvm. 



can run with considoral)le rapidity. The mouth-parts, in man}' speeies„ 

 nia}" be completely withdrawn into the body of the mite. The mandi- 

 bles are normally chelate, and the lingers toothed. Sometimes they 

 are greatly elongate and styliform, so fitted for piercing; in a few 



cases the moval)le tinger is lacking. In 

 many species thei-e is a projection or append- 

 age arising near the l)ase of the lingers 

 known sometimes as the ^' spur,'' sometimes 

 as the " Hagelluni." Beneath the mandibles 

 is a large piece, the hypostoma. It is bifid, 

 and each side ends in an elongate corneous 

 point. Between tlie two corneous points 

 is a long fleshy part, the lingula. The palpi 

 are prominent and usuall}' live-jointed. 

 Above the mouth there is in many forms 

 a thin plate, often toothed, known as the 

 epistoma. In the Uropodida', the palpi are 

 scarcely visible, as the body projects so 

 nuich in front. The legs are of moderate 

 length, usually slender, and arise close to- 

 gether, in a row each side. In the Uro- 

 podida^ the anterior pair is separated from 

 the others and their coxa are nearly con- 

 tiguous. The l)ody is commonl}' provided 

 with coriaceous plates or shields, the posi- 

 tion and shape of which are characteristic 

 of each species. These plates sometimes nearly cover the entire body. 

 Their position and names may be deserved from the accompanying 

 illustrations. There are some small shields or pieces which are often 

 of importance; a pair just behind the fourth coxiv are called the "meta- 

 podia;'] a pair just l)ehind 

 coxa? I are known as the 

 "■ jugularia,'' and a pair 

 behind sternal plate, the 

 "metasternalia." There are 

 frequently differences be- 

 tw^een the sexes in the ar- 

 rangement of the plates, and 

 in the males of many species fig- «7.-side view of a gamasus. e, epistome: p. peri- 



' treme; i', anal plate. 



the ventral plates are mostly 



coalesced. The female genital opening is commonly under the ante- 

 rior margin of a plate (the genital) which ends near the coxa^ of the 

 third legs. The male genital aperture is usually at the anterior mar- 

 gin of the sternal plate, only a short di.stance l)ack of the mouth. In 

 some groups, notably the Uropodida, tiie genital aperture of the 



Fig. t^O. — Venter of gamasus. a 



PERITREMi:; ?>,jrGULARIA; 0, STER 

 NAL PLATE: d, METAPODIA: f, GEN 

 ITAL plate; /, ANAL PLATE. 



