LAND CRUSTACEANS. 



71 



The legs (figs. 13 and 17) of the first pair are unequal, though both are chelate. The 

 larger, left chela, used for seizing and holding the food and as a weapon of offence and 

 defence, serves, when the animal is withdrawn into the shell, as a very perfect lid or oper- 

 culum, for which purpose its stout, rounded shape is clearly adapted. It may also {C. rugosus 

 A, fig. 17) bear a stridulating organ in the form of a series of parallel ridges on its outer 

 surface. The smaller chela is used for tearing the food and conveying the fragments to 

 the mouth. The second and third pairs of legs are adapted for walking. 



The hinder jmrt of the thorax, forming the middle of the three regions alluded to above, 

 may be said to begin at the level of the transverse portion of the cervical groove and to 

 include the two hinder pairs of legs. It is distinguished from the preceding region by 



Fig. 16. Mouth-limbs of the left side of Coeno- 

 hita cJypeatus from behind. A. Mandible ; B. 1st 

 maxilla ; C. 2nd maxilla ; D. 1st maxilliped ; E. 2nd 

 maxilliped ; F. 3rd maxilliped. A small portion of 

 the anterior side of D is attached to show the endo- 

 podite. 



In Payiinis the maxillipeds bear on their exopodites 

 long, slender, curved lashes, fringed with fine hairs and 

 much resembling those of many crabs. The absence of 

 these structures in GoenohiUi is perhaps due to the loss 

 of their functions in the absence of water. The little 

 backward hook on the first maxilla is wanting in 

 Pagurus. 



being rather depressed than compressed and by less strong calcification of its integument. 

 The branchiostegites, which anteriorly share in the general compression and calcification of 

 the body, are here soft and tend to be depressed. But the legs of the fourth pair are carried 

 pressed up against the sides of the body in such a way that the soft branchiostegites are 

 indented by them and only project dorsally and posteriorly where they overhang the limbs 

 in question. Behind, the branchiostegites gape widely from the body, and leave an opening, 

 through which the legs of the fifth pair can be thrust into the gill chamber. 



