I. '21. 



Key to the Genera of British Paguridea. 



I. Abdomen soft, twisted and adapted for living in a spiral 

 mollusc shell (Paguridae). 



A. Left cheliped larger than right ; a sharp movable 



rostriform process between ophthalmic scales 

 (Pagurinae) . . . . . . Diogenes. 



B. Right cheliped larger than left ; no movable 



rostriform process (Eupagurinae). 



1. No tube protrudes from opening on either coxa 

 of fifth pereiopods of male. 



a Paired pleopods, modified for sexual 

 purposes, usually present on first or 

 first and second abdominal segments ; 

 right sexual opening absent in female ; 

 fingers of cheliped move in a plane 

 oblique to the horizontal . . Parapagurus. 



b. No paired and modified pleopods on first 

 or second abdominal segments ; paired 

 sexual openings present in both sexes ; 

 fingers of cheliped move in a practi- 

 cally horizontal plane . . Eupagurus. 



2. A tube protrudes from opening on at least one 

 coxa of fifth pereipopods of male. 



a. A tube protrudes only from left sexual 

 opening of male and is bent outwards 

 in a semicircle ; no sexual modified 

 pleopods in female . . Anapagurus. 



h. Tubes protrude from both sexual open- 

 ings of male, the left short and directed 

 inwards, the right long and directed 

 posteriorly ; a pair of sexually modified 

 pleopods on first abdominal segment 

 of female . . Nematopagurus, 



II, Abdomen strongly calcified, pressed against sternum as 



in Brachyura (Lithodidae) . . . . Lithodes 



