Decapoda — Macnira. 53 



usually gL'oatly enlarged and very dissimilar in shape. Tlie second Table-case 

 legs are slender, and have the carpus, or " wrist," divided into ■'^°" ''^^ 

 many small segments. The members of this family are very 

 abundant in tropical seas, especially on coral reefs. Some of them 

 produce a clicking noise by snapping the fingers of one of the 

 chelae. 



In the family Palaemoitidae the first two pairs of legs end in 

 chelae, or pincers ; the second pair is larger than the first, and 

 has the carpus, or " wrist," undivided. The antennules bear eacli 

 tliree terminal filaments. To this family belong the common 

 marine " Prawns " of Britisli coasts and the " Eiver- Prawns " that 

 are abundant everywhere in fresh waters within the tropics. The 

 great size reached by some of the latter is shown by the specimens 

 of Palaejnon carcinus from the East Indies and P. jamaicensis from 



Fig. 33. 

 The common Prawn, LcaiuJcr scrrafits, slightly reduced. TTable-case No. 9.] 



the West Indies. Attention may also be directed to a specimen 

 of the conimon Prawn (Lcandcr scrratns) (Fig. 33) prepared by a 

 special process so as to retain the translucency of the living animal. 



In the family Cramjonidae the pincers of the first pair of legs 

 are imperfectly formed (sul>chelate) and much stronger than 

 those of the second pair, which are very slender. The rostrum 

 is usually short and flattened. To this family belong the common 

 Shrimp {Crangon vulgaris) and the large Arctic Shrimp (Sclero- 

 cramjon horcas). 



The Tribe Astacidea (or Nephropsidea) includes the true Table-case 

 Lobsters and Crayfishes. They may be recognised by having the '^"°' ^^■ 

 first three pairs of legs chelate or pincer-like, and the first pair 

 very large. 



The Lobsters constitute the iasVaWy Hom,aridae,QX\ the members 

 of which inhabit the sea. The last thoracic sternite is firmly fixed 



