CdMr.VRATIVE STUDY OF SHJlIBROID FLSTIES. 339 



but in Neothunnus it is nearly equal to or broader than the diameter of the 

 vertebral column, and it is still wider in Katsuiconus and Evlhynnus (figs. 57, g ; 

 58, g). In the Katsuwonidae the canal is separated from the vertebral column 

 by the development of a peculiar median process which I propose to name as 

 the epihaemjü process. These processes as well as the nem-al, and haemal 

 pi'ocesses ai'e more or less laterally compressed. The neiu-al and liacmal processes 

 are greatly bent backward near the distal end in vertebrae of the middle 

 l^art of the vertebral column. In Auxis the haemal canal is not closed in the 

 precaudal r^on. In Tlmnnus and Paraihunnns the haemal canal is closed in 

 the 10th vertebra ; but in Xeothunnm in the 11th. In the Katsuwonidae the 

 canal is closed still fiurther back : — In Katsuivonvs 12th, in Euthynnus 16th, 

 and in Auxis 21st. 



In the Thunnidae the first vertebra is very short, and is always anchylascd to 

 the occipital region with a zigzag sutm'e, so firmly that many authors overlooked 

 its centrum, though they found the detachable neural arch beloDging ,to it. The 

 anterior margin of the first nem-al spine is not straight, but notched. In 

 the vertebrae of the Thunnidae the longitudinal grooves are conspicuoas, 

 especially the lateral grooves. The vertebrae are massive, and are finely 

 striated at the surface, and the internal part is alveolar. The inferior 

 foramen as well as the haemal canal are very poorly developed in Thunnus 

 and Parafhitnmis ; but in Neothunnus they are well developed in caudal vertebrae. 

 In this fiimily the transvei-se process is develoj^jed from the fourth vertebra. 

 It is well developed in the following three to five vertebiue, as a short, nearly 

 flat process with a more or less trenchant edge. In the Elatsuwonidae the first 

 vertebra difiers but httle in size from the following vertebrae, and is less 

 firmly anchylosed to the skull, and at the same time the relation between its 

 centrum and the neiu'al process is much closer, not easily separating from each ' 

 other. The lateral gi'ooves of the vertebrae communicate with each other near 

 the axis in anterior veiiebrae of the precaudal r^ion, and in Euthynnus and 

 Auxia (fig. 15) the ridges between these grooves are poorly developed or 

 disappearing, thus the vertebral column is much more slender thiin in the 

 timnies. The mass of the vertebrae is greatly diminished, as the interior 

 alveolar part is nearly lost, leaving the hard, campact, cortical layer only. The 

 sm-fiice of the vertebrae is nearly smooth. The inferior foramen is enormously 



