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 branchiae is reduced 

 to nineteen on each side. 



These two genera, Homarus and Nephrops, therefore, 

 represent a famil}^ Homarina, constructed upon the 

 same common plan as the craj^fishes, but differing so 

 far from the Astacina in the structure of the branchiae 

 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 

 Potamohiidce than to that of the Parastacida, 



The Eock 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 antennae 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 Eock Lobsters are more 

 closely allied to the Parastacidce than to the Potamohiidce, 



