THE ROCK LOBSTER (PALINURUS). 261 
resembles the lobster in those respects in which the latter 
differs from the crayfishes: but the antennary squame is 
large; and, in addition, the branchial plume of the podo- 
branchia of the second maxillipede is very small or absent, 
so that the total number of functional branchie is reduced 
to nineteen on each side. 
These two genera, Homarus and Nephrops, therefore, 
represent a family, Homarina, constructed upon the 
same common plan as the crayfishes, but differing so 
far from the Astacina in the structure of the branchie 
and in some other points, that the distinction must be 
expressed by putting them into a different tribe. It is 
obvious that the special characteristics of the plan of the 
Homarina give it much more likeness to that of the 
Potamobiide than to that of the Parastacide. 
The Rock Lobster (Palinurus, fig. 70) differs much more 
from the crayfishes than either the common lobster or 
the Norway lobster does. Thus, to refer only to the more 
important distinctions, the antenne are enormous; none 
of the five posterior pairs of thoracic limbs are chelate, 
and the first pair are not so large in proportion to the 
rest as in the crayfishes and lobsters. The posterior 
thoracic sterna are very broad, not comparatively narrow, 
as in the foregoing genera. There are no appendages 
to the first somite of the abdomen in either sex. In 
this respect, it is curious to observe that, in contradis- 
tinction from the Homarina, the Rock Lobsters are more 
closely allied to the Parastacide than to the Potamobiide. 
