48 



THE VOYAGE OF H.M.S. CHALLENGER. 



The above description is taken from a male. In the female, which is of slightly arger 

 size, the spines on the carapace are comparatively more strongly developed. 



The following are the chief measurements in both sexes :- 



Breadth of carapace, . 



Length of carapace, 

 „ of rostrum, 

 ,, of right chelipede, 

 „ of first ambulatory limb, 

 „ of last leg-, 

 „ of abdomen, . 



Habitat. — Station 320, off Rio Plata ; depth, 600 fathoms ; bottom, green sand. 

 Two adult specimens (male and female), and two immature. 



Section B. PAGURODEA. 



Pagwriens, Milne-Edwards, Ann. d. Sci. Nat., ser. 2, t. vi. p. 262, 1836 ; Hist. Nat. des 



Crust., t. ii. p. 209, 1837. 

 Paguroidea, De Haau, Crust. Japon., p. 197, 1850. 



Paguridm, Dana, U.S. Explor. E.xped., vol. xiii., Crust., part. i. p. 401, 1852. 

 „ Stimpson, Proc. Acad. Nat. Sci. Philad., p. 70, 1858. 



Miers, Catal. New Zealand Crust., p. 01, 1876. 

 Haswell, Catal. Austral. Crust., p. 152, 1882. 



Carapace elongate, the part posterior to the cervical groove membranaceous, or less firm 

 than the anterior portion. Chelipedes and the two anterior pairs of legs well developed, 

 the ultimate and penultimate pairs of small size, and one or both usually chelate. 

 Thoracic sterna linear. Abdomen spirally twisted, or extended, and usually membranous, 

 the tergal elements as a rule rudimentary ; abdominal appendages present in both sexes, 

 consisting of a pair always present on the penultimate (sixth) segment, and of usually a 

 single biramous limb present only on the left side of the second to the fifth segments 

 inclusive, the first three of these well developed and ovigerous in the females. 



The Hermit Crabs occur in all seas from between tide marks down to very great 

 depths (over 2000 fathoms) ; they are most numerously represented, however, in shallow 

 water, and a few forms are even subterrestrial. Numerous structural modifications are 

 met with in the different genera, and these, as might be expected, are chiefly confined to 

 the form of the abdomen, that part of the body having suffered most from the curious 

 shell-inhabiting instinct noticeable in the majority of the species. There is every reason 

 to believe that the Hermit Crabs of the present day are descendants of a race of 

 Thalassinid-like ancestors, owing both their form and their persistence to the above- 



