INTRODUCTION. 



XV11 



segments with a terminal telson. The head bears a pair of eyes, 

 internal and external (or rather superior and inferior) antennae, 

 (1, 2) a pair of mandibles (Fig. vi., 3), two pairs of maxilla? 

 (4 and 5), and one pair of maxillipedes (6). The eyes are sessile 

 or unstalked, and consist of an aggregation of simple ocelli. 

 The internal or superior antenna? are very small in the Sand- 

 hopper, but maybe largely developed in its allies, and are formed 

 of a peduncle or stalk consisting of three joints and a short 

 flagellum. The external or inferior antenna? are much longer 

 than the superior pair ; their peduncle consists in the Sand- 

 hopper of three segments, but in the majority of its allies there 

 are five ; there is a long many-jointed flagellum. In front of 



Fig. vi. Appendages of the Sand-hopper (Talorchestia quadrimanaj 



magnified. 

 3, Mandibles; 4, first maxilla; 5, second maxilla; 6, maxillipedes; 

 7, first pair of gnathopoda ; 15, second pair of pleopoda. 



the mouth is a large movable labrum. The mandibles (Fig. vi., 3) 

 are strong triangular organs, with a toothed cutting apex and 

 internal grinding tubercle, and have no appendage in the Sand- 

 hopper. The maxilla? are delicate and foliaceous ; the first pair 

 (Fig vi., 4) consist of three plates armed with ciliated spines ; 



