Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

EarlyCretaceous Freshwater Fish Fauna in Kyushu, Japan 235
meristic characters and the characters of the head and caudal regions, but it differs
from P. kikuchii in the proportion. The body is slender and the depth is contained
4.7 to 5.5 times in the standard length in P. elegans, 3.2 to 3.7 times in P. kikuchii
(Tab. 6).
Order Gonorynchiformes ?
Family incertae sedis
(Figs. 94-95, PI. 59)
Specimen. KMNH VP 100,233, a specimen with its left side exposed. The head
region is missing. The length from the dorsal origin to the posterior end of the
hypural is 16.2 mm. The estimated standard length is 32.5 mm.
Locality. Minamigaoka (KM-1), Kokura-kita-ku (Kokura Northern Ward), Kita
kyushu City, Fukuoka Prefecture, Japan.
Horizon. The Third Formation (the upper formation, W3, correlated to the Lower
Wakamiya Formation) of the Wakino Subgroup in the Kwanmon Group, the Lower
Cretaceous.
Description.
The body is slender. The body depth is contained 7.6 times in the estimated
standard length. The outline from the occipital region to the dorsal origin is
straight. The dorsal fin is situated at about the middle of the body. The pelvic fin
is large and is situated below the dorsal fin (Fig. 94, PI. 59). The first dorsal fin
pterygiophore is inserted between the neural spines of the eighth and ninth abdomi
nal vertebrae. The dorsal fin is large and the base is longer than the anal fin base.
The anal fin base is contained 1.6 times in the dorsal fin base. The pectoral fin is
large and extends below the dorsal origin. The origin of the anal fin is behind the
end of the dorsal fin base. The caudal fin is forked. The number of principal
dorsal fin rays is 12. There are 12 dorsal fin pterygiophores. The number of
principal anal fin rays is 11. Thereare 11 anal fin pterygiophores. Twelve pectoral
fin rays are visible. Seven pelvic fin rays are visible. There are 19 principal caudal
fin rays (1,9,8,1). The total number of vertebrae is 35, with 18 caudal vertebrae.
There is a series of median supraneurals beginning immediately behind the head and
ending before the dorsal origin. Each supraneural is cylindrical. The neural arch
and spine of the first preural centrum are complete. There are 6 hypurals. The
first hypural is the largest. The second hypural is about half of the first one in width
and does not extend to the first ural centrum. There is a space between the second
and third hypurals. There are two ural centra. The second ural centrum bears
three hypurals (HYU3-5). One uroneural is visible and extends forward to the first