56 Proceedin./s of the Royal Irhk Academy. 



Chthonius. 



Ghthonius C. L. Koch 1843 (17). 



CephalothoTax usually broader in front than behind. Palps with fingers 

 long, in dorsal view sti'aight or nearly so, hand with 2 dorsal tactile hairs, 

 tibia caliciform. Galea present or absent. Eyes 4, 2, or 0. 



(Britannic species with eyes 4, cephalothorax always liroader in front 

 than behind, galea absent. All glossy, with large blackish bristles; without 

 granulation, more or less distinctly reticulate ; fused tergite-sternite of 

 abdominal somite XI. with perforation for somite XII. sub-ventral rather 

 near anterior ventral margin ; somite XII. with tergite and sternite separate, 

 stemite with 2, tergite without bristles ; chelicerae very large ; palps with 

 femur with an anterior row of 3 and an anterio-dorsal row of 5-6 

 bristles, tibia with large dorsal fissure ; hand without stalk, increasing 

 from broad base with more or less abrixpt anterior elbow ; the two dorsal 

 tactile hairs median ' ; teeth of fingers large, those of fixed finger • always 

 widely separated ; femur of legs IV. exceedingly deep ; coxae II. and III. each 

 with a l3ristle-group,; $ with genital-area conspicuous, plate II. with large 

 V-shaped opening with close-set marginal bristles and bounded anteriorly l^y 

 concave posterior margin of plate I. ; compared with ? , hand narrower, eye- 

 interval a little less, tubercle of movable finger of chelicerae smaller.) 



1. Hand with dorsal depression .... tetraclielatus. 

 Hand without dorsal depression ...... 2 



2. Posterior margin of cephalothorax with 2 large bristles . . 3 

 Posterior margin of cephalothorax with 4 large bristles . Bayi. 



3. Eye I. removed from front nearly or quite 1 diameter ; hand not 



darkened ....... ortJiodactylvs. 



4. Eye I. removed from front scarcely more than | diameter ; hand 



darkened ........ tenuis. 



C. Rayi L. Koch. 

 C. Bayi L. Koch 1873 (24).- Obisium orthodactylum Leach 1817 (13) ; in 

 part. 



Palps reddish-horny ; chelicerae rich reddish-brown, cephalothorax deep 



' The position of these tactile hairs, whether median, sub-median, basal or apical, and of the 

 hirge tibial fissure which tends to move in correlation, also the presence or absence of bristle-groups 

 ou coxae I. -111., provide useful specific chaiacters in Chthonins. 



-This common species was certainly not unknown wlien named C. Rrit/i hj h. Koch in 1873. 

 Chelifer ischiwclielus Herm. 180'! (8) and Chelifer trombidwides hsitr. 1804 (9) probably represent it, 

 but tlicse species cannot be certainly identified. Obisium orthodacti/liiiii Leach 1817 (13), in part at 

 least, represents it, three of Leach's specimens in spite of their bad condition being clearly 

 recognizable ; but as the one indicated as the type is perliaps doubtful, I have followed Cambridge 

 (42), who has identified it with the next species ; and as the present species is now universally known 

 as C. Kai/i L. Koch, tliat name is liere retained. 



