Sub-Gla?s 2. Malacostraca. 209 



filament, whilst a lamellate unjomted exopod very often arises from 

 its second joint; finally, a pair of powerful mandibles, with 

 frequently a three-jointed palp, and two pairs of maxillae, both of 

 a flattened form. The thorax, which is not sharply marked ofE from 

 the head, and whose segments (all, or a few) are often completely 

 fused, bears eight pairs of limbs, consisting typically {see 

 Fig. 150, 5), of a slender seven- j ointed endopod, the basal 

 joint bearing a flat, unsegmenfced epipod; whilst from the second 

 joint springs a usually narrower exopod, fringed with setee and 

 multiarticulate. Frequently either exopod, epipod, or both, are 

 wanting, and as a result of concrescence, the endopod may have fewer 

 than seven joints. The eight pairs of thoracic feet are seldom all 

 alike ; usually the flrst, or the first two or three, pairs are modified as 

 maxillipeds, subserving the functions of nutrition; whilst the 

 rest serve for locomotion, or are developed as prehensile organs. The 

 abdomen is typically seven-jointed; it is usually filled up with 

 powerful muscles, and forms a true locomotor apparatus, whilst 

 the viscera are for the most part located in the thorax. Each of 

 the six anterior segments usually bears a pair of appendages, the 

 abdominal limbs, consisting of a two-jointed peduncle and two 

 rami, the outer of which represents the exopod; these are 

 usually natatory organs (swimmerets). The last pair of 

 abdominal appendages is generally different from the rest ; it is 

 directed backwards, often broad, and with a short peduncle ; with the 

 seventh somite, which is always apodous, it frequently forms the caudal 

 fin. Amongst other characters common to the group, the following- 

 must be noticed : the region of the fore-gut following the short 

 ■oesophagus forms a gizzard, lined with chitin, and furnished with 

 hard denticles and with setse. The rest of the digestive tract is 

 tubular ; the anus is on the ventral surface of the last abdominal 

 segment; the liver, which is composed of a number of tubes, opens 

 into the gut behind the gizzard; the heart is usually short and wide, 

 sometimes more elongate, and almost always provided with three (or 

 fewer) pairs of ostia ; the ovaries are generally partly fused; the 

 •oviducts are, however, separate, and open on the under side of the 

 ante-penultimate (sixth) thoracic segment, or on the basal joint of its 

 appendages; the testes are usually like the ovaries ; the seminal 

 ducts open on the last (eighth) thoracic segment, or on the basal 

 joints of the eighth thoracic limbs. 



Note. — The genus Nebalia forms a transition from tlie Entomostraca, and 

 especially the Phyllopoda, with which it should he grouped, to the Malacostraca. 

 It lives in the Mediterranean, the North Sea, on the coast of Greenland, and 

 elsewhere. The body is divided into head, thorax, and abdomen ; the thorax is 

 eight-jointed, with eight similar pairs of appendages, which are like those of 

 other Phyllopoda. Each appendage (Fig. 150 A) is seven-jointed, lamellate, with 

 broad exo- and epipod. The abdomen is eight- jointed, and, as in the Phyllopoda. 



