The Osteoloffv of the Scombridse. 03 



"to 



fin are detached and the two portions of the vertebral column are 

 diiferentiated only by the attachment of these elements. The para- 

 pophyses are nowhere large, iind the first one large enough to consider 

 occurs on the ninth or tenth vertebra, though there are three or four 

 bony tubercles developed anterior to this. The parapophyses bend 

 down and join to form haemal arches at about the middle of the 

 abdominal cavity. The first two vertebrae bear epipleurals only. The 

 anterior ribs fit in sockets in the vertebrae, but posteriorly where the 

 parapophyses are developed the ribs are attached to their tips, so 

 when the former unite to form haemal arches the bases of the opposite 

 ribs are brought in contact. The ribs are all directed backwards so 

 that they lie close together. The epipleurals are developed back to 

 the caudal keel, and are all on the centra of the vertebrae, so are 

 remote from the ribs where the ribs drop down to the tips of the 

 parapophyses or hiemal spines. The zygopophyses are well developed 

 along the greater part of the column, but toward the tail they become 

 very small and neural and haemal processes take their place. These 

 posterior spines are broad and flat, and each are laid firmly down over 

 the next succeeding vertebra apparently'restricting the vertical motion 

 of the tail. A wide keel is developed on the side of the caudal 

 peduncle, and a urostyle is present on the hypural plate. The forked 

 caudal rays nearly cover the hypural plate from sight. The baseosts 

 are much expanded laterally at the base of the dorsal spines. The 

 interspinous rays of the vertical fins are crowded together and have 

 well developed lateral wings, but they are not connected to each 

 other by bony wings. 



THUNNUS. 



A specimen of Thunnus alaluuga (Gmelin), 35 inches in lengtti, from San 

 Diego, California, and a liead of a large specimen of Tlinnnus thynnns (Lin- 

 naeus), QYj inches long, from the tip of the vomer to the end of the basi- 

 occipital, from San Francisco. 



In this foi-m the ethmoid is produced to a median angle in front, 

 and the nasals project far anterior to it. The supraoccipital crest 

 projects back in a spatulate process unattached below to the exoc- 

 cipitals. The epiotics meet broadly, but a slender spur of bone sent 

 down from the supraoccipital to the exoccipitals covers the suture 



