59. 福島市附近第三紀層産魚類化石に就いて

抄録

(1) The Geological Outline
Fossil fishes of the Scombridae were found at Iwayakannon, Sinobuyama in the suburbs of the city of Hukusima. Sinobuyama, a solitary hill in the Hukusima basin, is 273 in. high above the sea level, and about 200m. higher than the basin floor. It is mostly composed of the massive liparitie tuff, partly agglomeratic, and its lower part of alternation of tuffaceous sandstone and shale, containing plant fossils. The fishes were found associated with plants in a horizon. The stratigraphical relation of this fossil horizon with Yanagawa shell bed, north-east of Hukusima basin, cannot actually be determined. However, I agree with TSUJITA in that this horizon will be younger than the Yanagawa shell bed.
(2) The Fossils
The number of the fossils collected is about 50. Thes fossils are of the same species. The result of my measurement is shown in the table. The length of the fossil is about. 40cm., and its form resembles that of Scombridae fish. The body (the caudal fin excluded) is 3.7 times as long as the head the thickest part of the body is a little posterior to the base of the first dorsal fin, and is 0.7 times as long as the head. The height of the head is about half of the length of the head. The pectoral fins consists of 3 spinous and 15 soft rays the length is equal to the distance from the pectoral fins to the base of ventral fins. The ventral fin consists of 7 rays and it is sorter than the pectoral fin. The first dorsal fin is above or slightly in front of the ventral fin, its spines have 12 rays. The second dorsal fin is above the anal fin, and it has one spine and 12 soft rays. It has 5 finlets. The anal fin has one spine and 11 soft rays. The caudal fin is about one tenth as long as the total length of the fish, and it is deeply forked with 38 rays. The mouth is large, about one third of the head, and both jaws have small teeth. The vertebrae consist of about 12 abdominal vertebrae and 18 caudal vertebrae.
This Scombridae fish is distinguished from the present Scomber japonicus HOUTTUYN, (though the two resemble each other) by the fact that the former is more slender than the latter, and that the pectoral fins grow more in front than the latter
Recently NIINO, has reported about Scombridae fish found in Gumma prefecture. Although the precise accounts were not described, the facts that the fossils are found in a great number in one horizon and that tuff is above the fossil bed, are noted. D. S. JORDAN reported the discovery of the Scombridae fish in Miocene of Southern California, but none of my specimens agrees with his. This fish is eventually cited as Scomber sp.