33<> F. P. SMITH ON SOME BRITISH SPIDERS TAKEN IN 1905. 



Oedothorax gibbosus (Bl.), 1841. 



18-11. Xeriene gibbosa, BL, Trans. Linn. Soc. 



1841. ,, tuberosa, BL, Trans. Linn. Soc. 



1864. „ gibbosa, BL, Spid. G. B. I. 



1864. ,, tuberosa, BL, Spid. G. B. L. 



1879. ,, gibbosa, 'G&mb., Spid. Dorset. 



1879. ,, tuberosa, Cainb., Spid. Dorset. 



1900. Gongylidium gibbosum, Camb., List Brit. Irish Spid. 



1900. ,, tuberosum, Camb., List Brit. Irish Spid. 



1904. Oedothorax gibbosus, F. P. S., Journ. Quekett Club. 



1904. „ tuberosum, F. P. S., Journ. Quekett Club. 



This small but striking species occurs not uncommonly in one 

 restricted area in Epping Forest. Invariably associated with it 

 is the spider known as Oedothorax tuberosus (BL). A very careful 

 examination of extensive series of specimens of O. gibbosus and 

 O. tuberosus has led me to the conclusion that their claim to 

 being distinct species is very doubtful. In each of several col- 

 lections made in Epping Forest the proportion of gibbosus to 

 tuberosus was about equal. The females were numerically about 

 equal to the sum total of the males, but the most critical 

 examination failed to reveal any characteristic by means of which 

 they might be separated into two species or varieties. The 

 epigynum is very constant in form, differing slightly, but dis- 

 tinctly, from that of 0. fuscus or of 0. retusus. It is, however, 

 of very simple structure, and would be less likely therefore to 

 exhibit any considerable variation. In fact, it could with some 

 reason be argued in support of the specific distinctions of gibbosus 

 and tuberosus that the females are indistinguishable purely by 

 reason of the simplicity of their structure. 



At first glance, the two forms of male appear totally different. 

 In gibbosus the cephalo-thorax is strongly elevated near its 

 centre, forming a very distinct, obtusely rounded eminence. 

 The anterior side of this eminence is deeply excavated, the cavity 

 being covered with a plentiful supply of blackish hairs. In 

 tuberosus the eminence is of somewhat similar form, but lacks 

 the characteristic excavation in front. The difference is a 

 striking one, and I have never met with a form which could be 

 regarded as absolutely intermediate. On the other hand, the 

 palpal organs appear to be absolutely identical in the two types. 



