80 FISH GALLERY. 



the body is somewhat compressed laterally and of moderate 

 ' vertical depth, and is covered with rhombic scales ; the dorsal fin 

 does not extend more than half the length of the trunk ; all the 

 fins have large fulcra. The gape of the mouth is small, the jaws 

 and vomer are provided with several rows of teeth, more or less 

 conical. The vertebrae have either half-centra or ring-centra 

 only, the notochord being evidently largely persistent in adult 

 life. The parietal bones meet in the middle line. The range of 

 the family is from the Upper Permian to the Cretaceous. 



In the family Pycnodontidse also the body is compressed, 



Pycno- high and oval, with rhombic scales, which, however, are in some 

 8e ' cases wanting in the hinder part of the body. The pelvic fins are 

 small, the dorsal and anal fins are more or less extended, and 

 the fin-rays robust ; there are no fulcra. There are no vertebral 

 centra, the notochordal sheath being apparently without any 

 ossifications. The opercular apparatus is reduced; there is no 

 jugular plate ; the parietal bones are separated by an occipital 

 plate. The gape of the mouth is small, the dentition consists 

 of prehensible teeth on the premaxillary and dentary bones, 

 and oval teeth adapted for crushing on the vomerine and splenial 

 bones (see 225). The family ranges from the Lower Lias to the 

 Lower Eocene; the principal genera are Gyrodus (224, Gyrodus 

 circularis, from the Lithographic Stone of Bavaria), Mesturus, 

 Mesodon and Pycnodus. 



The Eugnathidse, e. g. Eugnathus orthostomus, 226, are a 

 family of fishes which must have been predatory, judging from 

 their large, strong mouth and their teeth, the marginal ones of 

 which are conical and larger than the inner teeth. The body 

 is long and not much laterally compressed, the scales are rhombic, 

 the fulcra large, the fin -rays robust, the dorsal and anal fins 

 short-based. The vertebral centra are rarely more than incomplete 

 rings (hypocentra and pleurocentra alternating), two such rings 

 to each vertebra. The opercular apparatus is complete, with a 

 single jugular plate ; the prem axillae are in contact. The family 

 ranges- from the Trias to the Cretaceous. 



AmiidEe The family Amiidse is a small one containing the living Amia, 

 a fish which in structure approaches more nearly to the Neichthyes 



