METAZOA CRUSTACEA. 335 



form of leaf-like, gill-bearing thoracic legs (fig. 3). The 

 eight abdominal segments are also distinct. The first 

 four of these carry each a pair of swimmerets consisting 

 of a basal stem and two leaf-like parts (fig. 4) ; the fifth 

 and sixth pairs of appendages are small, and the last two 

 segments are without swimmerets, though the terminal 

 segment carries a pair of spines. There is no telson in 

 Nebalia, and in this respect the genus differs from most 

 Crustacea. 1 



The segments of the head are consolidated, but as 

 there are six pairs of cephalic appendages it is inferred 

 that this region of the body is made up of as many seg- 

 ments. The dorsal and lateral portions of these segments 

 have grown backward forming the carapace which not 

 only covers the thoracic region but also four of the abdo- 

 minal segments, as already stated. In front, a movable 

 plate, called the rostrum, is hinged to the carapace which 

 the animal can move up and down at pleasure. The 

 appendages of the head are a pair of eye-stalks and two 

 pairs of well developed antennae (fig. 2), a pair of mandi- 

 bles (fig. 5), and two 2 pairs of maxillae (figs. 6, 7), mak- 

 ing six pairs attached to the head. 



Stomatopoda. The young of Squilla, first described as 

 Alima (PI. 826, fig. i, Squilla empusa Say), has a long, 

 loosely articulated body. The posterior thoracic segments 

 are not covered by the carapace and these segments are 

 without appendages, none being developed after the large 

 grasping legs which correspond with the second pair of 

 maxillipeds.3 The flat abdomen is greatly extended and 

 bears a few pairs of swimmerets. 



1 According to Claas (Ann. and Mag. Nat. Hist., (6), III, 1889, 

 p. 441) the last two segments of the abdomen represent the telson 

 of the Malacostraca. 



2 Lang says one pair, making five pairs to the head. Packard 

 describes and figures six pairs (i2th Ann. Rep. U. S. Geol. and 

 Geogr. Surv., 1878, part i). Woodward says three pairs of mouth- 

 parts (Quart. Journ. Geol. Soc. London, LI, 1895, p. Ixxxiv). 



3 Faxon, Mem. Mus. Comp. Zool., IX, no. i, 1882, explanation 

 of PI. vii. 



