33 FISHES OF SINALOA. 405 



On the upper part of the operculum is a large scale- 

 like bone. 



The suborbitals arc well developed and plate-like, ex- 

 tending back nearly to the posterior edge of the preopercle. 



b. Vertebral Column. 



There are forty-two vertebra- in the spinal column. 



The first vertebra is co-ossified to the skull, and appar- 

 ently bears no ribs: the second vertebra supports a pair 

 of very small, slender ribs, which articulate directly with 

 the sides of the vertebra : the third vertebra supports the 

 first pair of large ribs: they are articulated with the trans- 

 verse processes. 



The first fourteen or fifteen neural spines and pairs of 

 transverse processes are articulated with the vertebra' by 

 sutures, thev are easily separated from the vertebra' by 

 boiling or maceration. 



The vertebra gradually increase in size and reach their 

 largest size about two-thirds of the distance from the an- 

 terior to the posterior end of the spinal column, where 

 they are three or four times the size of the anterior ones. 

 This character is more marked in the adult than in the 

 young. 



c. Shoulder Girdle. 



The shoulder girdle is exceedingly well braced, the 

 post-temporal is widely forked, and strongly articulated 

 to the epiotic processes of the skull. 



The supra-clavicle is long and slender, its posterior face 

 is hollowed out and attached some distance from the upper 

 end of the clavicle, which projects upward. 



This projecting upper end of the clavicle is braced to 

 the skull by two long bones.* The first bone is very 

 slender, at its anterior end it is connected to the exocci- 



* See Dr. R. W. Shufeldt's report on the osteology of Amia calva; Bull. 

 U. S. F. C, 1883, page 59. 



