Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

182 Yoshitaka Yabumoto
Horizon. The horizon at Kumagai is the Fourth Formation (the uppermost forma
tion, W4, correlated to the Upper Wakamiya Formation) and the horizon of Minami
gaoka is the Third Formation (the upper formation, W3, correlated to the Lower
Wakamiya Formation) of the Wakino Subgroup in the Kwanmon Group, the Lower
Cretaceous.
Etymology. The species is named for Mr. Tateyu Aoki, who collected and donated
the specimens to the Kitakyushu Museum and Institute of Natural History.
Description of the holotype.
The body is slender and the body depth is contained 6.4 times in the standard
length. The head length is contained 4.4 times in the standard length. The median
fins are relatively posterior in position. The dorsal origin is behind the anal origin
and about vertical with the anterior one fourth of the anal base.
The first dorsal fin
pterygiophore is inserted between the fourth and fifth caudal vertebrae. The dorsal
fin base is about half of the anal fin base. The pectoral fin elongates and extends
over the middle of the abdomen. The pelvic fin is not preserved on the holotype.
The caudal fin is forked. The number of principal dorsal fin rays is 11. There are
12dorsal fin pterygiophores and a stay. The number of principal anal fin rays is 22.
There are 21 anal fin pterygiophores. The principal dorsal and anal fin rays are
preceded by three small unbranched accessory rays respectively. Twelve pectoral
fin rays are visible. The total number of vertebrae is 48, with 23 caudal vertebrae.
The anterior end of the vertebral column is not visible. The number of abdominal
vertebrae was estimated on the basis of the ribs. The number of ribs is 23. There
is a seriesof median supraneurals beginning immediately behind the head and ending
above the first caudal vertebra. Each supraneural of the anterior two-thirds is wide
and leaf-shape with a ridge running from a dorso-posterior corner to an anteroventral
corner (Fig. 52).
The gape of the mouth is large. The lower jaw is long. The dentary bears
small canine like teeth on its oral margin. The suture between the dentary and
anglo-articular is not visible and the posterior part of the lower jaw is poorly
preserved. The mandibular sensory canal runs within thedentary. The premaxilla
has canine like teeth which are larger than those of the dentary. The posterior end
of the lowerjaw is placed below the center of the orbit. The maxilla is not visible.
There are villiform teeth on the endopterygoid. Teeth are not visible on the
parasphenoid. The frontal is long and carries a superficial long groove (Fig. 54).
The first preural centrum bears the narrow parhypural. The neural arch and
spine of the first preural centrum are complete. There are seven hypurals. The
first hypural is the largest. The second hypural is about halfof thewidth ofthe first
one in width. There is a space between the second and the third hypurals. The