ARTICULATA. 115 



eyes are pedunculated. Tliis order contains the largest of the Crustacea, 

 as the lobsters and crabs. 



Latreille divides this order into two families, named sub-orders byWestwood 

 and tribes by Burmeister, who includes them with the Stomatopoda in his order 

 PodopTithalma^ and gives each of these an equal rank with the Stomatopoda, 

 Isopoda, and other orders. Milne Edwards divides the Decapoda into three 

 sections, admitting the Brachjura and Macrura^ but separating certain 

 anomalous genera from both, but chiefly from the Macrura^ to form the third 

 section Anomura (also written Anomoura^ and meaning, the tail anomalous). 



In the Anomui'a the cephalothorax is large, the abdomen is not fully 

 developed, and is much like that of the Brachyura. The second pair of 

 external antennae are well developed, the external foot-jaws are generally 

 like feet ; the three or four anterior pairs of feet are generally like those of 

 the Brachyura, and adapted to locomotion, but the remaining ones are 

 rudimentary, and in some cases used only for holding. 



Fam. 1. PaauTidm. The genus Pagurus {j^l. 7S, fig. 10), and several 

 others of the same family, are remarkable for having the abdomen weak 

 and soft, and the two posterior pairs of feet much reduced in size, and not 

 adapted for walking. These animals are protected by the empty spiral shell 

 of a mollusc, and as they increase in size they crawl along the beach 

 hunting a larger shell, and various trials are made until a suitable one is 

 found, the old one being again and again resumed, until the animal has 

 suited itself. The abdomen and small feet enter the shell, and when the 

 animal wishes to be safe, it withdraws itself so far that the head and robust 

 anterior feet close up the aperture like an operculum. The posterior 

 extremity of the body is curved, and with the posterior feet, adapted to 

 maintain the shell in a proper position. One of the anterior pair of feet is 

 larger than the other, and both terminate in a pair of pincers or chelae. 

 The sub-families are PaguriiicB^ Hippince^ and Porcellaiunce. 



Fam. 2. Raninidce. In Ranina {R. serrata., pi. 78, fig. 9) the carapace 

 is roughly serrated and transversely truncated before and narrowing pos- 

 teriorly, producing a sub-triangular form. The anterior feet are cheliform, 

 but not of a very large size, and the succeeding feet have the tarsus or last 

 articulation lamellar. The abdomen is narrow, of seven articulations, tlie 

 last ones bent downwards. The species figured inhabits the East Indies, 

 and is said to crawl up objects, even to the tops of houses. The sub-families 

 are: Dromiinai^ Homolincc., and Raninlnce. 



The Macrura are named from having a large and well developed tail or 

 abdomen, ending in a fan-shaped fin {p)l. 78, figs. 11-14). The form is 

 generallj^ elongated, the carapace longer than in the crabs, and generally 

 armed with a frontal spine; and the species, with few exceptions, are 

 marine. The antennce are in general long, the first pair not received into 

 a cavity as in the crabs ; the mandibles are well developed ; the walking 

 feet are slender, and the first and second pairs frequently cheliform. The 

 abdomen has seven articulations, of which the five basal ones bear the false 

 feet. The caudal fin is formed of five pieces, the middle being an extension 

 of the seventh or last segment, whilst the lateral ones arise from the sides of 



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