THE DECAPOD CRUSTACEA. 199 



bristles. The rostrum is shorter than the stalk of the outer 

 antennae. The abdomen has six joints in both sexes, the 

 legs are about four times the length of the carapace, are 

 very slender, hairy, and usually covered with weed. 

 Another species occurs in deeper water. 



The other genus Inaclms is represented in shallow 

 water by /. dorhynchus, found occasionally beneath stones. 

 The carapace differs from that of StenorhyncJius in being 

 sub-triangular, nearly as broad as it is long, with short, bifid 

 rostrum. The eyes are retractile, and the orbits elongated, 

 instead of circular. The species is characterised by three 

 spines on the gastric region of the carapace ; of these two 

 are anterior and one posterior, the three forming a triangle. 

 There is another species of larger size, but it occurs in 

 deeper water. 



The next family of crabs is that of the Cyclometopa, or 

 crabs with rounded forehead. In them the carapace is 

 broad and arched in front and narrows posteriorly; in its 

 whole shape it contrasts markedly with that of the spider- 

 crabs. The common shore crab is an admirable and easily 

 obtainable example of this family, and in it the general 

 characters may be readily observed. Notice how very 

 different is the shape of the carapace from that of the 

 spider-crabs. The rostrum has disappeared, and in its place 

 we have a rounded region between the eyes known as the 

 forehead. From the eyes the margin of the carapace slopes 

 outwards and backwards, and is strongly toothed; this is 

 the antero-lateral margin. Next, the margin slopes inwards 

 and backwards, this region being known as postero-lateral ; 

 it is untoothed. Finally, the two postero-lateral borders are 

 united by a line, the posterior margin. It will be noticed 

 that the carapace is here broad in front, where in the 

 spider-crabs it is narrowest, and narrows behind where that 

 of the spider-crab broadens out. Most of our commonest 

 crabs belong to this family, and as these are largely dis- 

 tinguished by the shape and teeth of the carapace, it is 

 worth while being clear as to terminology before beginning 

 the study of the individual crabs. 



The Cyclometopa are distinguished from spider-crabs not 

 only in general shape, but by the swiftness of their move- 

 ment s and their high intelligence. Quick at offence and 



