THE LOBSTER AS A TYPE OF CRUSTACEA 33 



marus, and the American as Homarus americanus. 

 The so-called " Norway Lobster " or " Dublin 

 Prawn," which differs from the Common Lobster in 

 having large kidney-shaped eyes and long and 

 slender claws, and in many other details of structure, 

 is placed in a distinct genus, and is known as Nephrops 

 norvegicus. The genera Homarus and Nephrops, 

 together with some others, constitute the family 

 Homaridae, which again is grouped with other 

 families in a tribe, Nephropsidea, forming a part 

 of the order Decapoda. These groups are intended 

 to express the varying degrees of resemblance and 

 difference in structure between the species of animals 

 which make up the class Crustacea. Since we have 

 good grounds for believing that all these species have 

 arisen by some mode of evolution, this classification 

 also represents the varying degrees of actual rela- 

 tionship between the different forms, so far as this 

 relationship can be discovered. In the next chapter 

 a brief sketch of the chief subdivisions of the 

 Crustacea is given, with such details as to the 

 characteristics of each as are necessary to render 

 intelligible the succeeding chapters on their habits 

 and modes of life. 



