94 Edwin Chapin Starks. 



between them. There is a deep pit or infolding of the bone on the 

 lower surface of the cranium between the pterotic, the prootic, and 

 the sphenotic, just inward from the condyle of the hyomandibular. 

 It extends upward, so that the prootic is in contact with the epiotic 

 on the inner surface of the cranium, and tlie pterotic is thus com- 

 pletely excluded from the brain chamber. There is a large, trian- 

 gular, smooth opening into the brain chamber just behind the frontal 

 on each side of the supraoccipital crest. The alisphenoids are joined 

 together in such a way at the median line that the anterior opening 

 into the brain chamber is divided into a small one in front of their 

 union and a little larger one behind. The myodome opens through a 

 long slit in the side of a very large conical chamber in the para- 

 sphenoid. This chamber in a cranium measuring 5I/2 inches in length 

 is an inch long and nearly half an inch broad across its mouth. 

 The opening in its side from the myodome does not extend quite to its 

 tip. The vomer bears an elongate patch of teeth. The suborbital 

 bones are similar to those of Scomberomorus, but the cheek scales that 

 border the eye are much thicker. 



The vertebrae number 40 with the hypural plate ; in this specimen 

 as in our specimen of Sarda the ribs and anal fins are detached and 

 it is impossible to distinguish the caudal from the abdominal vertebrae 

 without them. On the fifth vertebra the first parapophysis appears ; 

 on the next three it has increased very rapidly in size, and extends 

 straight out laterally; on the ninth vertebra its ends bend abruptly 

 downward, and on the tenth it has united with its opposite fellow 

 to form a broad round haemal arch without a spine. On the eleventh 

 vertebra a hsemal spine appears and the bases of the opposite ribs 

 are brought in contact with each other as in the other members of 

 its family. The inferior postero and antero-zygopophyses are equally 

 developed, arching towards each other each as a sharp spur. There 

 is no inferior foramina in the base of the haemal arches. The superior 

 zygopophyses, the ribs and epipleurals, and the other elements not 

 mentioned are as in Sarda. 



The skull of Thunnus thynnus differs from that of T. alalunga in 

 having the parasphenoid developed upward in a broad wing to meet 

 the descending wing from the basiphenoid, and a descending wing 

 developed from the union of the alisphenoids. 



