80 



WITH HARD CHEEKS. 



ACANTHOPTERYGII. WITH HARD CHEEKS. 



THE HALF-ARMED STICKLEBACK. 



Gasterosteus semiarmatus, Cuv. et Valenc. Hist. Nat. des Poiss. t. iv. p. 493. 



This species is distinguished from the preceding by the 

 want of the arming by defensive plates along the sides of 

 the tail, and in having rather larger teeth ; in other respects 

 it does not diifer much, and may be considered by some as 

 only a variety or the young of Gasterosteus trachurus, that 

 had yet by increased age to acquire the requisite number of 

 lateral plates. I have, however, taken specimens of all sizes, 

 which were uniform in the number of lateral plates, and close 

 examination by a friend, who has paid particular attention to 

 this subject, has shown that no point of ossification or indu- 

 ration is to be found posterior to the last perfect lateral plate, 

 which seldom passes beyond the line of the vent. The 

 figure makes farther description unnecessary. The number 

 of fin-rays are 



D. 111+ 10 : P. 10 . A. 1 -1-9 : C 12. 



It occurs in similar situations to the other Sticklebacks, 

 but not always in company with them. 



