226 THE VOYAGE OF H.M.S. CHALLENGER. 



duty of a tongue in passing and keeping the food between the grinding tubercules of the 

 mandibles, and the portion which covers the apparatus anteriorly aids the double meta- 

 stoma posterior to the mandible in enclosing the organs of mastication within a mem- 

 branous orifice, whose margins undoubtedly fulfil the duties of lips. The mandibles carry 

 an appendage which differs in form and size in several genera, but is never more than two- 

 jointed in any genus of the tribe ; generally they are larger and longer, and apparently 

 of more importance and use, than in the Trichobranchiata or the Phyllobranchiata. In 

 those species of Penaeidea where it is large, broad and foliaceous, it suggests that the habit 

 of the animal is, while swimming, to feed on small creatures, that are by means of these 

 large, spreading plates directed within its mouth. I have proposed to use the term 

 synaphipod for this appendage rather than any other suggested, because it can, I 

 think, be readily demonstrated to be the continuation or representative of the joints of 

 the true appendage, and not a branch of it. 



The next pair of appendages is the first pair of siagnopoda, which bears a resemblance 

 to the type of the same pair of organs as seen in the young and undeveloped forms of the 

 Astacidea and the Brachyura. It consists of three joints, two of which are broad and 

 foliaceous, having their inner margins fringed with hairs, while the third or outer is 

 narrow, and in some species single-jointed and terminating in a point, in others two- 

 jointed, the second joint tapering and tipped with a few hairs. 



The second and third pairs of siagnopoda, although varying specifically in form, 

 are yet modifications of the same general type as in other groups. 



The second pair consists of three branches, two of which are flat and foliaceous, 

 generally longitudinally divided, and having their inner free margins fringed with hairs ; 

 the third is subcylindrical, varies in length specifically, and sometimes consists of three or 

 four joints, and on the outer margin is a broad mastigobranchial plate that varies in 

 form in different species. The third pair perhaps undergoes more change than the 

 second, but still retains the same fundamental plan of arrangement, consisting of one 

 large foliaceous branch furnished on the inner free margin with hairs, a subcylindrical one 

 formed of several articulations, and on the outer side at the base a long and broad masti- 

 gobranchial plate that is transversely divided into an anterior and a posterior portion. 



The two pairs of gnathopoda are the anterior appendages belonging to the pereion, 

 and assume a greater or less pediform character all through the tribe. 



The first pair is generally broader and has the fourth joint or meros long and the 

 ischium short ; the second joint, or basis, carries a long multiarticulate branch, and 

 the coxa supports a long mastigobranchial plate, to which a podobranchial plume is in 

 some genera attached. The three terminal joints lie reflexed against the inner side of 

 the preceding ones, and the inner or antagonising margin is invariably furnished with a 

 mat of strong hairs, among which stiff spines are occasionally intermingled. The entire 

 organ bears a close resemblance to the same appendage as it exists in the higher Brachyura. 



