THE CLASSIFICATION OF CRUSTACEA 59 



tribes. The Penceidea include the large Prawns of 

 tropical seas {Penceus — Plate IV.), which have the 

 first three pairs of legs provided with chelae, and 

 not differing greatly in size. The Stenopidea are a 

 small group of forms resembling the Penmdea in 

 having chelae on the first three pairs of legs, but the 

 third pair are much larger than the others. The 

 Caridea comprise our common Prawns {Leander, 

 Pandahis) and Shrimps (Crangon), besides a host of 

 less generally known forms ; in these the third legs 

 are never chelate, although the first and second 

 often are. 



The second suborder, that of the Reptantia, 

 is much more diversified, but the animals composing 

 it are united by certain characteristics, of which the 

 most obvious are their creeping habits (although 

 some species can swim well), their heavily armoured 

 bodies, often more or less flattened from above 

 downwards, with the rostrum never thin and saw- 

 edged, and the swimmerets not used to any great 

 extent for swimming. 



The first section of the Reptantia, the Palinura, 

 includes the Spiny Lobsters, Rock Lobsters, or Sea- 

 Crawfish, and their allies, forming the tribe Scylla- 

 ridea. They are distinguished by having no large 

 pincer-claws, though the last pair of legs may have 

 small pincers in the female sex. One species, the 

 Common Spiny Lobster (Plate V.), is found ion the 

 southern and western coasts of the British Islands. 



