432 KAMAKICHI KISHIXOÜYE: 



Key to the families of the order Pleeostei. 



Itody wholly covered with scales, second dorsal and anal high, vertebrae 18 f 21. 

 transverse process ]iresent. 1st vertebra short, anchylosed to the bkull. alis- 

 phenoids meet at the ventral median Hne. nir-bladiler generally present Thunrüäae. 



Body naked outside of the corselet, second dorsal lower than the first, 

 vertebrae generally 20 + 19, some intermuscular bones are divided into two, 

 distal and proximal, epihaemsl spine developed between the centrum and 

 the haemal arch in most vertebrae, network of haemal processes well 

 developed, air-bladder wanting . . Kntsuxcorääae ■ 



Family THUNNTDAE Kishinouye. 



Thunnidae, Kishinouye, 1918. 



Body plump, wholly covered with scales, which differ in size and form in 

 different pai'ts of the lx)dy. Corselet well developed, but its boandaiy is not 

 distinct. The lateral line has a peculiai' cmTe above the pectorals. Teeth 

 rather feeble. Single series of small conical teeth in both jaws. They are sharj) 

 and averse inward. "VilHform teeth on the vomer, palatines, and pterygoids. Many 

 dentigerous calcareous plates are found on the palate. The denticles on these plates 

 are quite similai- to those found on the vomer, palatines and pterygoids. Thus 

 the roof of the mouth-cavity is quita rough, contraiy to the nearly smooth roof in 

 the Katsuwonidae. Thi'ee lobes of the Hver subequal. Intestine rather long, with 

 three folds. Pyloric tubes developed only on the posterior convex side of tha 

 duodenum. Pyloric coeca heterochtic, irregular in size. Those foimd at the 

 distal end being longer and thicker than those at the proximal part. Tliis 

 heterochrony is more marked in primitive forms. Rectum short, it hns nearly 

 the same diameter as the preceding part of the intestine. Aii-bladder pi-esent, 

 except in Neothunmis varus. 



Cutaneous blood-vessels above and Ijelow the lateral median line ai'e unite<l 

 both at the anterior and posterior ends, and are connected, by shoii horizontal 

 vessels with the chief blood-vessels in the haemal canal at the caudal pedimclo. 

 The cutaneous veins ai"e large and unite with the Cnvieriiiai ducts directly or ■with 

 the cardinal vein. Each of the paired cutaneous arteries ai'ises just liehiud the 

 plaryugeal muscles or somewhat behind it^ runs backwiu'ds and downwards 

 behind the root of either the third or fifth rib, and is divided into two nearly 

 parallel branches, a little before it comes tj the surface of the muscle, between 

 two consecutive intermuscular bones. Tlie dark red portion of the lateral 



