XII. — CRUSTACEA AND LOWER INVERTEBRATA. 93 



Sub-class V.—DECAPODA, or ten-footed Crustacea, has 

 the branchise enclosed in a special cavity on each side of the body ; 

 and five pairs of legs, the first of which terminates in two-fingered 

 claws. The sub-class is divided into three orders : — 



1. Brachyura (short-tailed). — The abdomen is short and 



reduced to a triangular or rounded tail without caudal fin, 

 and is sunk into an excavation on the ventral surface of the 

 thorax. Stenorhynchus Jissifrons, Uyastenus diacanthus, 

 Para7nithraxsternocostulatus,Pa7^theno2)eliorrida,Ateragatis 

 Jloridus, Thalamita crucifera, Gelasimus vocans, Talitrus 

 sylvatics, Grapsus variegatuSjCalcq^i^a hepatica, And Leucosia 

 sple7idida, are examples of the principal families. (See 

 Cases 13 and 14). 



2. Anomura (irregular-tailed). — The abdomen is but 



slightly developed, except in the Paguridce. Dromia 

 excavata, Lomis hirta, Remij^es testudinaria, Ranina dentata^ 

 Eui^aguius sinuatus and the great land crab Birgus latro 

 are examples. (See Cases 11 and 13). 



3. Macrura (long-tailed). — The abdomen is strongly devel- 



oped, provided with four or five pairs of abdominal feet, and 

 terminating in a well-developed five-parted tail. Examples : 

 Galathea australiensis, Ibacus j^eronii, Palinurus hugelii, 

 Astacojjsis serratus, Alpheus edioardsii, and PencBUS canali- 

 culatus. (See Case 12). 



Sub-Kingdom III— VERMES, or WORMS. 



The classes into which this sub-kingdom is divided are widely 

 different from each other, and within our limits little information 

 can be given about them. The body is generally soft, elongate or 

 vermiform, bilaterally symmetrical, with or without feet, which, 

 when present, are never jointed. Specimens of the most 

 important will be shortly exhibited. 



Class I.— The PLATYHELMINTHES are more or less 

 flattened worms of a very simple organisation, and without any 

 true sec;ments. There are three orders in this class :— 



