ON THE BRITISH EDRIOPHTHALMA. 33 



strongly defined where their office is most required, but absent where not 

 wanted. 



In some, as Anonyx denticulatus, the anterior teeth are reduced to a 

 smooth cutting edge ; but we have failed to detect that any relative form is 

 dependent upon the character or kind of food which it may be the habit of 

 the animal to prey upon. The Talitri, which are known to be carnivorous, 

 appear to differ in no important feature from those which are believed to live 

 on marine vegetables, as is the case with the Gammari. 



The ischium being developed into the necessary or important part of the 

 mandibles, the remaining articulations of the typical appendage are reduced 

 to an obsolete form, and in some of the Amphipoda are entirely wanting. 

 This is the case in the family of Orchestidm, a circumstance from the, at 

 most, amphibious character of the group, which suggests the idea, that it is 

 efficient only to those which inhabit the water, from scarcely any of which 

 among the Amphipoda is it wanting, as far as our experience goes. The use 

 of this appendage is, perhaps, to direct floating material more readily towards 

 the mouth. The organ generally is raised and lies between the lower pair 

 of antennae. 



The MaodllcB. — These are separated from the mandibles by a posterior 

 l&bium (PI. XV. fig. 2), which differs from the anterior in being cleft in the 

 centre, but probably cooperates with the mandibles in the process of man- 

 ducation. 



The maxillae are two pairs, the first or anterior, and second or posterior. 

 They are extremely delicate leaf-like organs, and by no means fulfil the idea 

 suggested by their name. 



The segments of which they are appendages, together with the next suc- 

 ceeding, the first maxilliped, are fused together and concentrated around the 

 mouth. 



Thejirst maxilla consists of three foliaceous plates (Edwards has figured 

 a fourth in this same species. Gam. lociisia) ; the basal is developed upon 

 the second articulation or basis joint of its homological position of the leg ; 

 the coxa being, we presume, suppressed from a tendency we observe in 

 Crustacea generally to a fusion of this articulation with the main trunk of 

 the animal, rather than with the appendage of which it forms a part. The 

 second foliaceous plate is developed upon the third joint or ischium in the 

 homological character of the leg, and therefore represents the veritable por- 

 tion of the mandible (PI. XV. figs. 3, 4, No. 5). The third leaf-like plate con- 

 sists of two joints, the fourth and the fifth, the meros and the carpus. This 

 last represents the appendage to the mandibles vvith the anterior joint or pro- 

 podos suppressed. The extremity of each plate is fringed ; in the anterior 

 or third it exists in the form of five or six short stout teeth. Tlie middle have 

 likewise teeth, but these are more numerous, and exist in two rows ; the 

 teeth are long, and each has the point slightly curved, having the anterior 

 edge itself furnished with three or four smaller teeth. The first or posterior 

 plate is furnished with a thick row of hairs, the anterior portion of which 

 is extremely plumose and bushy. 



The second maxilla consists of two foliaceous plates only, wliich latter 

 homologize with the first and second of the anterior maxilla ; they are 

 extremely delicate and furnished on their anterior margin with stout hairs, 

 which generally are slightly ciliated. 



In the genus Sulcator (but whether it holds through the whole of the 

 subfamily of the Pontoporeides, we have not experience to guide us) the 

 posterior plates of both pairs of maxillae are folded so as to become two or 

 three parallel leaves, one of which, in the first maxilla, is developed into a 



1855. D 



