Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan 121
Description of the holotype.
The presumed body depth is moderate. The dorsal fin is situated at about the
middle of the body. The dorsal fin base is longand its length is contained 1.4 times
in the body depth. There are 14 dorsal fin rays with 4 fin fulcra. The first fin
fulcrum of the dorsal fin is short and its length is about one third of the second fin
fulcrum. The second fin fulcrum is about half of the third fin fulcrum. The third
fin fulcrum is about one third of the fourth fin fulcrum. The scales of caudal part of
the body are rhombic. The number of scales from the dorsal margin to the ventral
margin at the caudal immediately behind the dorsal fin is 11 to 13.
Remarks. The family Semionotidae of the order Semionotiformes has two genera,
Semionotus and Lepidotes, and the Semionotidae share the presence of dorsal ridge
scales and a large posteriorly directed process on the epiotic (Olsen and McCune,
1991). The presence of dorsal ridge scales and a large posteriorly directed process
on the epiotic are unknown, but the present fossil is similar to Lepidotes yungkangensis
(Chang & Chou, 1974) from Early Cretaceous deposits of Zhejiang Province in
China in the position of the dorsal and pelvic fins, the number and the form of fin
fulcra of the dorsal fin, the form of scales and the number of scales from the dorsal
margin to the ventral margin at the caudal immediately behind the dorsal fin. But
L. macropterus differs from L. yungkangensis in the number of dorsal fin rays and the
length of the dorsal fin base. The number of dorsal fin rays is 14 in L. macropterus, 9
in L. yungkangensis. The length of the dorsal fin base is contained 1.4 times in the
body depth in L. macropterus, 3.0 times in L.yungkangensis.
Subdivision Halecomorphi
Order Amiiformes
Family Amiidae
Genus Nipponamia gen. nov.
Diagnosis. It differs from other genera of the Amiidae in having the combination of
following characters. The gular plate is almost rhombic in the ventral view. The
premaxillary teeth are larger than teeth on the dentary and the number of teeth is 4.
The margin between the condyles of the hyomandibular for the neurocranium and
the opercular process is narrow and deeply concave in V-shape. The ventral end of
the hyomandibular is divided into two parts. The number of vertebrae is numerous
and 75 including ural centra. The length of vertebral centra is shorter than the
depth. The ural centra are slightly curved upward. Ganoid scales are absent.
Type species.
Nipponamia satoi sp. nov.
Etymology.
The generic name, Nipponamia consists of Nippon meaning Japan, and