87 



of defensive plates along the sides of the tail, and by the 

 somewhat larger size of the teeth; in other respects it 

 differs but little, occurring in similar situations, and fre- 

 quently in the same shoal. The fin-rays are — 



I). III.-I-10: P. 10: A. 1+9 ; 0. 19. 



THE SMOOTH-TAILED STICKLEBACK. 



(^Oasterosteus Idums*.) 



This species is distinguished from those preceding it by 

 the side armour-plates, ten in number, extending no further 

 than the ends of the rays of the pectoral fin, — the whole 

 length of the body behind these being smooth and soft, and 

 without scales. 



Fin-rays: D. HL + IO: P. 11: A. 1 + 8: C. 12. 



* leiwus, smooth-tailed, from leios, smooth, and oura, a tail, Gr. 



