( -^ ) 



The condition of the thoracic sterna varies greatly ; sometimes they 

 are broad and almost crab-Iikc, sometimes they are almost linear, occa- 

 sionally their development is not quite bilaterally symmetrical. 



The abdomen also varies considerably. In the majority of the sub- 

 order it is less well developed than the cephalothorax, and is soft— the terga 

 being insufficiently developed to cover its surface — asymmetrical, and coiled 

 in adaptation to the spiral curve of the gastropod shell which the animal 

 commonly uses as a portable habitation. In a few cases (Pylochelidcs) it is 

 larger than the cephalothorax, perfectly straij^ht and symmetrical, and has 

 all its terga well formed and efficient. In certain forms, that protect 

 themselves with something other than a rigid shell, the abdomen, while 

 remaining soft, becomes merely fiexed ; and there are a few forms that are 

 independent of any adventitious protection and have a more or less crab-like 

 abdomen. Occasionally the abdomen is rudimentary. Regarded in a general 

 way the Pagurine abdomen is no longer of any use in locomotion, but 

 has become an envelope for certain important viscera (liver and reproductive 

 glands). 



2. The Appendages. 



The eyestalks are well formed and mobi'e, and it is rare, even among 

 hermit-crabs that live in the abysses to which no sunlight can penetrate, 

 to find the eyes defective. The coxal joint of the eyestalk is usually sur- 

 mounted, dorsally, by a prominent platelet or spine — the "ophthalmic scale." 



The antennular peduncles are carried folded, when pulled out they, as a 

 rule, considerably exceed the antennal peduncles in length : their first joint 

 is dilated at base: their flagella are usually short, and the upper one is much 

 longer than the lower. 



The joints of the antennal peduncle are 5 in number. The 2nd joint 

 often has its outer distal angle spiniform, and usually also carries an 

 acicle — the homologue of the large antennal scale of Nephrops — which is 

 generally mobile and often of considerable length. 



The mouth-parts in the main resemble chose of Nephrops (see Fasc. I, 

 pi. A, fig. I), but in the ist maxillae the endopodite (palp) is, oftener than 

 not, non-flagellate ; in the 2nd maxilla- the scaphognathite is • posteriorly 

 more or less truncated ; in the first maxillipeds the exopodite is often 

 non-flagellate; and there are no epipodites to the ist and 2nd maxillipeds, 

 and no podobranchise on the 2nd and 3rd maxillipeds : moreover, the flagella 

 of the exopodites of the maxillipeds are bent sharply inwards as in crabs. 

 The coxopodites of the 3rd (external) maxillipeds may be in contact, or 

 may be separated by a broad sternum — a point of primary importance in 

 the classification of the group, as Bouvier has insisted. 



