32 INVERTEBRATE ZOOLOGY. 



Order 2. Stomatopoda Carapace involving five thoracic seg- 

 ments, five pairs of maxillipeds. and 

 three pairs of legs. Gills iipon the alv 

 dominal appendages. ifSquilla. 



Order 8. Schizopoda Carapace invoh-ing entire thorax, eight 



pairs of two-branched, gill-bearing, tho- 

 racic legs, no maxillipeds. -^ 3Iysis. 



Order 4. Dekapoda Carapace large and heavy, invohang the 



entire thorax, six pairs of maxillipeds and 

 five pairs of legs, of which the first bears 

 a heavy claw. Gills at base of thoracic 

 feet upon the sides, protected by the edge 

 of the carapace. 



Sub-order 1. Macnira Abdomen elongated, bearing appendages. 



if Ho>uani.<!. 



Sub-order 2. Bnichyura Carapace generally broader than long. 



\\'ith grooves for the reception of the 

 short antennae and ej'es. Abdomen re- 

 duced, and folded back over the sternum. 

 if Cancer. 



SUPPLEMENT TO THE CRUSTACEA. 

 TRILOBITEA. 



An important group of fossil forms, presenting stnne superficial resemblance 

 to the Isopods. They are oval and flattened in form, and possess a dorsal car- 

 apace, divided by two longitudinal gi-ooves into three areas, one median 

 (rhachis) and two lateral {pleurae). The carapace consists of a cephalo- 

 thorax, and a variable number of segments, of which the anterior ones are 

 free-moving, and termed the '' thorax." followed by several fused ones, the 

 •• abdomen" or pygidinm. 



The cephalo thorax consists of a central piece (glabeUHin), and two lateral 

 pieces, the fixed and movable cheeks, between which are a pair of compound 

 eyes. 



