OJMPARATIVE STUDY OF SCOMBROID FLSHES. 433 



muScle is rather uarrow, and moots tiiu nxinl skeleton with 11 ihutow neck or 

 root in the hyp:i.xial \X)rtion (jnly. 



Ligament in a deep median groove between the anterior end of tiir. 

 fi"ontal8 is attached to the skin, anterior to the median foramen of the sknU. 

 Tlu's ligament is a cliai'acteristic of this family. 



The transversa process of some precaadal vertebrae is broad, well developed. 

 The first vertebra is greatly reduced in height and firmly anchylosed t) the 

 skull. Inferior foramen is small, and is fonnd in the caudal vertebrae only. 

 Number of vertebrae is constant, 39 in tatjd, of which 18 are precaucLd, and 

 21 caudal. The haemal canal is closed in the tenth or eleventh vei-tcbra, i. e. near 

 the middle of the precaudal region. Alisphenoids meet at the ventral meditui 

 line. Anterior precaudal vertebrae, are broader than Ingh. lioof of the moutli 

 cavity is coveretl with numeroiB plates covered with villous teeth. 



Many systematists put too much weight on the length of thi; pect;jrals, 

 but it has little value in the classification. 



Key to the genera of Thunnidae. 



Cutaneous blood-vessels pass through the myotome of the fifth vertebra, surface 



of the liver striated with fine venules T/iunnus. 



Cutaneons blood-vessels pass through the myotome of the seventh vertebra, 

 surface of the liver not finely striated with venules. 



Posterior cardinal vein is not continuous with the Cuvierian ducts. 



Vascular plexus on the inner side of the liver Parathunnus. 



Posterior cardinal vein is continuous with the Cuvierian ducts, vascular 



plexu& in the haemal canal Neothunnus. 



Gemis Thunnus Smth. 



Thunnus South, 1845. 



Thynnus, Cuvier, 7817; Günther, 1860. 



Orcynus, Cuvier, 1817. 



Germo, Jordan, 1888. 



Albncora, Jordan, 1889. 



Body plump, robust. The firat liaemal cauid is closed in the tenth vertebra. 

 Anterior liaemal arches of the precaudiil region ai"e turned forward and naiTow. 

 Eight side of the stjmach receives an artery fi-om the downward branch 

 of the coeliaoo- mesenteric arteiy. Two large branches of the coeliaco-mesenteric 

 artery send their blootl to the liver, and they are finely divided into plexas 

 ou the inner side of the Uver. These plexus reunite inta saveral artaries to 



