EXERCISE IX. 
THE SHORE CRAB. 
Sub-kingdom—ARTHROPODA. Class—CRUSTACEA. 
Sub-class—PODOPHALMATA. 
Order—DECAPODA: Five pairs of legs; branchie enclosed in the carapace. 
Tribe—BRACHYURA: Abdomen inflexed beneath the body ; antenne short ; 
fourth and fifth pairs of legs not raised above the others, and not. 
chelate. 
1. External characters.—Kill the crab by immersion in 
weak spirit. The upper surface is almost entirely 
covered by a hard shell—the carapace. On the 
anterior margin are the eyes at the tips of their 
peduncles, which are lodged in cavities in the cara- 
pace. That portion of the carapace between the 
orbital cavities is called the front. The carapace is 
divided into regions, named from the organs that le 
below them. The central portion, behind the front, 
is the gastric region, on each side of which lie the 
right and left hepatic regions. The centre of the 
carapace is the genital region, and the posterior 
the cardiac region. The two lateral portions, behind 
the hepatic regions, are the right and left branchial 
regions. On turning the animal over, the cara- 
pace is seen to be inflected anteriorly on each side 
of the mouth, forming the sub-hepatie, or ptery- 
gostomian regions. Posteriorly the carapace 1s ope 
on each side of the abdomen, forming the afferent 
