IXTRODUCTION. 



This volume is the First Part of a monograph of the Decapod Crustacea of 

 that part of the Oriental Eegion of Wallace which Kes within the political 

 boundaries of British India. 



The Decapoda belong to the subclass Malacosfraca of the Crustacean kind, 

 the Crustacea being one of the main branches of the great phylum Arthropoda. 



In the members of this phylum, which also includes the Xipliosura, the 

 Arachiida, the Millipedes, the Centipedes, and the Insects, the body consists of a 

 series of segments or somites carrying jointed or segmented appendages. Though 

 the segments — with the pair of appendages which each one typically carries 

 — may vary greatly in actual form, yet they are all built on one and the same 

 fundamental plan, and the superficial layers of the integument, both of the 

 somites and of the appendages, are more or less completely hardened, by chitin 

 or by salts of lime, so as to form a rigid exoskeleton, which during growth is 

 periodically moulted. 



Among the Arthropoda the Crustacea are recognized by the fact that while 

 they possess antennae, as do the air-breathing Insects, Centipedes and MilUpedes, 

 they typically breathe in water by means of gills connected with the appendages, 

 as do the non-antennate king-crabs {Xiphosura) . Their spermatozoa are non- 

 motile, like those of Millipedes. 



Among the Crustacea the Malacostraca are distinguished by the fact that 

 the body is made up of a definite and constant number of segments. 



The characters that separate the Order Becapoda from the other ordei's of 

 Malacostraca will be understood if we examine, in some detail, a typical member 

 of the Order. 



The type usually selected is the European Crayfish, Astacus fluviatilis : the 

 type here chosen is the Andaman Lobster, Nephrops andamanica, as belonging to 

 the local fauna. 



As far as tbe general construction of the body, the general modifications of its appendages, 

 and the general relations of the viscera go, any of the common species of freshwater or murine 

 prawns (Palsemon, Feneus) may be used for dissection if Nejihrops is not procurable. 



