The Osteology of the Scombridse. 97 



are expanded to accommodate it, though there is no well separated 

 parasphenoid chamber as in Euthynnus and Thunnus. Between the 

 prootic and alisphenoid there is a narrow infolding of the bone to 

 form a deep groove. 



The supraoccipital widely separates the parietals, but does not 

 altogether separate the epiotics, which meet broadly behind it. There 

 is no opening into the brain chamber behind each frontal, and the pit 

 behind the prootic shows no tendency to break through the top of the 

 cranium. The lateral process of the parasphenoid attaches to the 

 prootic above but along its posterior edge is an opening into the 

 myodome. 



The auxiliary maxillary is as broad as the maxillary and nearly 

 half as long. The teeth on the jaws are very small; there are none 

 on the vomer or palatines. The third and fourth suprapharyngeals 

 are covered with moderate sized teeth, and they are a little less closely 

 attached to each other than in Scomber. On the second pharyngeal 

 the teeth are very small and set in a small patch, which is scarcely 

 differentiated from the other dentiferous plates that cover the inner 

 surface of the arches. The other characters of the skull, and shoulder 

 and pelvic girdles are essentially as in Euthynnus. 



There are 22 abdominal vertebrse and 15 caudal, or a total of 38 

 with the hypural. The abdominal region is very much longer than 

 in Scomber, and a most extraordinary modification has taken place in 

 some of the inferior processes of the vertebrae. This condition will 

 best be appreciated if studied from behind forward. On the fourth 

 caudal vertebra the processes are normal ; a hsemal arch of moderate 

 size springs directly from the lower surface of the vertebra, and 

 terminates in a long hsemal spine. From the front of the arch the 

 antero-zygopophysis meets the postero-zygopophysis of the preceding 

 vertebra; each forming half of a sharp spur. On the next vertebra 

 the antero-zygopophysis and the base of the arch have enlarged into a 

 single, solid, bony pedicle carrying the haemal arch away from the 

 body of the vertebra. The pedicle gradually increases in length until 

 at about the beginning of the posterior third of the abdominal cavity 

 the haemal arch is distant from the body of the vertebra a distance 

 equal to twice the length of a vertebra. The haemal arch is nowhere 



