GAMMARIDEA. 



849 



much longer (that is, vertically). The fifth on either side in the 

 Orchestiae is generally about as long anteriorly as the fourth, and 

 near its middle or just posterior, it narrows, and there is a second 

 rounded lobe, about half the length of the anterior. In the Allor- 

 chestes, the fifth epimeral is abruptly much shorter than the fourth. 

 The epimerals may be quite naked, or sparsely edged with minute 

 hairs or setules; they are rarely sculptured or sulcate, and in this 

 case, the bases of the six posterior legs, which are large and broad, 

 have similar markings. 



Hoimlogies of the parts of the head.— On pages 23 to 28 of this 

 Report, we have pointed out the subdivisions of the carapax, espe- 

 cially its anterior and buccal portions, in the Brachyura; and we 

 now turn to the head of the Orchestidse, taking these as the type of 

 the Amphipoda. Figures 1 i, k, I, on Plate 57, represent the head 

 of the Orchestia {Talitrus) insculpta of the author, in different positions, 

 ^g. i, representing a side view; k, a front view; I, an under view (the 

 front part or extremity of the maxillipeds being towards the observer) ; 

 in, a view of the back part of the head below the ventral surface ad- 

 joining. Like parts are lettered alike in all these figures. 



In figure h (the front view), md, m\ ra 2 , m\ are respectively the 

 mandibles, the first maxillae, the second maxillae, the maxillipeds, as 

 they lie in sight, in their natural position; and a\ a 2 , are the bases of 

 the two pairs of antennae. The same parts are lettered by the same 

 letters in figures i and I, except that the antennae are, of course, not 

 shown in an under view (fig. Z), and they are added in full in the 

 lateral view (fig. i). 



Again, in figure k (with which the other figures should be com- 

 pared), the areas of the shell or surface are— b b', the top of the head 

 and upper part of the sides of the head ; c, an area adjoining the 

 antennae, having a membranous covering, and properly a part of the 

 base of the outer antennae ; d, a shelly area either side of e or epi- 

 stome ; Z, what is called the labrum, situated between the mandibles. 



The epistome (e) is subtriangular in form. It extends upward to a 

 narrow point between the antennae ; and below on either side it is 

 prolonged by a narrow process. This process is united at its extre- 

 mity by a suture with a piece/, of similar width. This piece/, as 

 seen on figure i, extends backward, on the sides of the head, forming 

 an area directly below b', with which it coalesces posteriorly. 



213 



