CRUSTACEANS. DEC APOD A. 73 



female carries them for a time suspended under the abdomen, 

 or even enclosed in a kind of pouch formed of appendages of the 

 legs ; sometimes the young are born in this pouch, and remain in 

 it until after they have undergone the first moult. 



11. The CLASS OF CRUSTA'CEA is divided into three natural 

 groups or divisions, according to the conformation of the mouth ; 

 namely, 



1st. The Trite! res or Grinders, haviag the mouth furnished with 

 jaws and mandibles proper for mastication. 



2d. The Sucto'ria or Suckers, having a mouth provided with a 

 tubular beak armed with suckers. 



3d. The Xi'phosura (from the Greek, xiplws, a sword, and 

 oura, tail), in which the mouth is destitute of the appendages pro- 

 perly belonging to it, but is surrounded by legs, the bases of 

 which constitute the jaws. 



12. The group of TRITO'RES or Grinders is divided into nine 

 orders, and comprises most of the crusta'ceans. The principal 

 orders are named Decapoda, Isdpoda, Am'phipoda, &c. 



LESSON VII. 



CRUSTA'CEANS. ORDER OF DECAPODA its Division. 



BRA'CHYU'RA. Crabs Land-crabs Habits. 



ANOMOU'RA. Soldier or Hermit-crabs. 



MACROU'RA. Craw-fishes Lobsters Locuske Prawns. 



ORDERS OF AM'PHIPODA and ISO'PODA. Sea-louse Wood-louse 



King-crab Entomo 'stracans Trilobites. 

 CLASS OF CIRR'HOPODA. Ana'tifa J3ala'nus. 



I. The order of DECAPODA (from the Greek, deca, ten, and 

 pouSj foot) is so called, because the animals comprised in it have 

 ten legs. These crusta'ceans (fig. 63) have the head and thorax 

 confounded in one piece, and concealed under a kind of shield, 

 called carapace (fig. 61, a). The eyes are borne on movable 

 peduncles, and the branchiae are situate on each side of the thorax, 

 enclosed in particular cavities beneath the lateral parts of the 

 carapace (Jig. 62, br). The mouth is armed with six pairs of 

 jaws ; the first pair are named mandibles ; the two next are jaws, 

 properly so called ; and the three last are termed foot jaws. In 



II. How is the class of Crusta'cea divided ? 

 12. How is the group, of Trito'res divided ? 



1. What are the characters of decapods? 



7 



