436 ARACHNIDA CHEKNETIDEA CHAP. 



Classification. -The order Chernetidea consists of a single 

 family, Cheliferidae. Nine genera are recognised by most 

 authors, but their grouping has been the subject of a good deal 

 of difference of opinion, largely dependent on the different 

 systemic value allowed by various arachnologists to the absence 

 or presence of eyes, and to their number when present. Simon 

 takes the extreme view that the eyes are only of specific value, 

 and he is thus led to suppress two ordinarily accepted genera, 

 Chernes and Roncus, which are separated chiefly by eye-characters 

 from Chelifer and Obisium respectively. He relies rather on 

 such characters as the presence or absence of galea, epistome, and 

 trochantin, and establishes three sub-families as follows : 



(i.) CHELIFEHINAE. Galea. No epistome. Trochantin on 

 all legs. Eyes two or none. Sole genus, Chelifer (Chelifer 

 + Ghernes). 



(ii.) GARYPINAE. Galea. No epistome. Trochantin on legs 

 3 and 4 only. Eyes four or none. Genera Chiridium, Olpium, 

 and Garypus. 



(iii.) OBISIINAE. No galea. An epistome. No trochantin. 

 Genera Chthonius and Obisium (which includes Roncus}. 



Whatever be the value of the eyes in the classification of this 

 group and Simon adduces strong arguments for his view 

 there can be no doubt of their convenience in practical identifica- 

 tion. Moreover, as 1'ickard-Cambridge 1 points out, a grouping 

 of the genera according to the eyes results, as regards British 

 species, in pretty much the same linear arrangement as Simon's 

 classification, and it may therefore be convenient to mention that, 

 of the six genera represented in this country, Chthonius and 

 Obisium are four-eyed, Roncus and Chelifer two-eyed, while 

 Chernes and Chiridium are eyeless. 



Sub-Fam. 1. Cheliferinae. These Chernetidea have the 

 cephalothorax slightly narrowed in front, and generally marked 

 dorsally with two transverse striae, while the abdominal plates 

 are bisected by a dorsal longitudinal line. "With the exception of 

 Chelifer cancroides, which is always found in houses, all the 

 species are to be sought under bark, though occasionally they are 

 discovered under stones. 



The two genera of this sub-family are Chelifer and Chernes, 

 the species of Chelifer being two-eyed, and those of Chernes blind. 

 1 Monograph of the British Species of Chernetidea, Dorchester, 1892. 



