314 Mr. R. I. Pocock on Liphistius. 



bellata into Artionycha and Peiissonycha and Ausserer's 

 subdivisions of Thevaphosidse into Dionycha and Trionycha 

 may not represent natural groups. 



The principal divisions of the Aranese that I here propose 

 may be diagnosed as follows : — 



a. The spinning-appendages retain their embryonic 

 position in the middle of the lower surface of 

 the abdomen ; there are eight spiuning-mam- 

 millfB. The upper surface of the abdomen is 

 furnished with nine distinct tergites and the 

 lower with two distinct sternites. The cephalo- 

 thoracic sternum is extremely narrow as com- 

 pared with the width of the carapace Mesothelae. 



Fam. LiphistiidcB. 



h. The spinning-appendages migrate to the posterior 

 end of the abdomen ; there are never more than 

 six distinct mamiuillaj. The abdomen is never 

 provided with distinct tergal plates, and the 

 abdominal sternites persist only as the pulmo- 

 nary opercula and P the epigyne. The cephalo- 

 thoracic sternum is much wider as compared 

 with the carapace Opisthothelae. 



a'. The plane of the joint of the mandible with 

 the ceplialothorax is nearly vertical, the fang 

 closing almost directly backwards. Four 

 lung-sacs, the posterior widely separated, 

 close behind the anterior, and with distinct 

 opercula. Usually only four, rarely six 



vspinning-mammillas Mygalomorph.«!. 



Fam. Aviculariiflcs, Atypidce. 



h'. The plane of the joint of the mandible with 

 the cephalothorax nearly horizontal, the fang 

 closing obliquely inwards and backwards. 

 The posterior lung-sacs almost always re- 

 placed by tracheal tubes ; when retained, as 

 in Hypochilus, they are situated in the middle 

 of the abdomen and covered with a con- 

 tinuous fold of the integument. With six 

 spinning-mammillse ; not uncommonly the 

 fourth pair found in Liphistius is retained 



as the ci'ibeUum Aeachnomobph^. 



Fam. Hypochilidcf!, Dysderidcs, 

 FilistatidcBf Drassidce, &c. 



