82 Edwin Cliapin Starks. 



shows, however, a much closer alliance with the latter sub-family 

 than with the former. 



Thnnnus (the genus Germo is not here recognized as distinct) 

 is plainly close to Auxis and Euthynnus, as is shown by the exclu- 

 sion of the pterotic from the brain cavity, and in nearly all char- 

 acters but the condition of the infra-vertebral processes. It is rather 

 astonishing to find genera running so close together as these three 

 do, and yet differing so radically in the condition of the hsemal arches. 



Liitken*" calls the iieculiar condition of the inferior vertebral 

 processes in Auxis a modification of the condition of these processes 

 in Euthynnus. This can scarcely be so, as the modification, though 

 as extraordinary in Auxis as in Euthynnus, is of a different char- 

 acter. It is difficult to imagine either condition as being a modification 

 of the other. It seems probable that these two genera left their parent 

 stem at about the same place, or in other words that they are both 

 a modification of some similar condition in the common ancestor 

 from which the development has been divergent. 



In Euthynnus the inferior vertebral foramina and the h?emal 

 arches are enormously developed, the latter springing almost directly 

 from the centra of the vertebra^, while both the postero and antero- 

 zygopophyses equally form long slender processes between the arches. 



In Auxis neither the haemal arches nor parapophyses are enlarged, 

 and they are borne far away from the body of the vertebrae each by 

 a solid bony pedicle formed (at least in part) by the antero-zygo- 

 pophysis ; the postero-zygopophysis taking no part in this formation. 



So to consider the condition of Auxis as a modification of that of 

 Euthynnus we should have to eliminate the postero-zygopophyses 

 together with the laminse of bone that incloses the inferior foramen 

 behind each arch, join the antero-zygopophyses and the bone sur- 

 rounding the front of the inferior foramen into a solid pedicle, and 

 restrict the great arch to a small opening at the distal end of the 

 pedicle. 



The foregoing may be summed up by the following diagram show- 

 ing the supposed origin of the genera. 



'Spolia Atlantica, p. 596, 1880. 



