192 



HIGH SCHOOL ZOOLOGY. 



Ffg. 120.— Camharus robuatus. (Girard). 

 l>ut all are included in the genus Cambarus, while those on the 

 Pacific slope of the Rocky Mountains, as well as the European 

 crayfishes, belong to an allied genus, Astacus- This genus gives 

 its name to the family Astacidse, which includes the lobster 

 ( Jlomarus americanus), the marine representative of the crayfish. 

 Any species will serve for making out the arthropodous charac- 

 ters already mentioned, as well as those peculiar to the Crustacea 

 which follow. 



'4. Twenty segments, of which only the last (telson) is desti- 

 tute of a pair of appendages, are invariably present in the ^roup 

 of Crustacea, to which the crayfish belongs, and these are 



