154 CRUSTACEA——EUCARIDA—_—DECAPODS: CHAP. 
Tribe 1. Nephropsidea. 
This tribe includes the Lobsters and Crayfishes, animals well 
known from their serviceableness to man. There are three 
families, which will be treated separately. 
Fam. 1. Nephropsidae. The podobranchs are not united 
with the epipodites, and the last thoracic segment is fixed and 
fused to the carapace. The chelae are generally asymmetrical. 
The most important Lobsters are the European and the American 
species—Homarus vulgaris (= Astacus gammarus) and H. ameri- 
canus respectively ; these animals engage a large number of people 
in the fisheries. It is estimated that in America about £150,000 
are spent every year on Lobsters. 
The genus Nephrops contains the small Norwegian lobster 
and other forms. 
Herrick’ gives some interesting particulars with regard to 
the life-history of the American species. The largest recorded 
specimen weighed about twenty-five pounds, and measured twenty 
inches from rostrum to tail; similar European specimens have 
been recorded, but, on the average, they are not so large as the 
American forms. 
The Lobster, like all Crustacea, undergoes a series of moults 
as the result of increase in size, shedding the whole of the 
external integument in one piece. This is accomplished by 
a split taking place on the dorsal surface at the junction of 
thorax and abdomen; through the slit so formed the Lobster 
retracts first his thorax with all the limbs, and then his abdomen. 
When first issuing from the old shell the animal’s integument is 
soft and pulpy, but the increase in size of the body is already 
manifest ; this increase per moult, which is approximately the 
same in young and adult animals, varies from 15 to 15 per cent of 
the animal’s length. According to this computation, a Lobster 
2 inches long has moulted fourteen times, 5 inches twenty times, 
and 10 inches twenty-five times, and it may be roughly estimated 
that a 10-inch Lobster is four years old. Young Lobsters 
probably moult twice a year, and so do adult males, but females 
only moult once a year soon after the young are hatched out. 
The process of moulting or ecdysis is an _ exceedingly 
1 Bull. U.S. Fish Commission, xv., 1895. 
