180 



SUB-CLASS GAXOIDEI. 



Fam. 2. Sphaerodontidae. Very similar to preceding ; with obtusely 

 conical or chisel-shaped teeth. Trias to Chalk. Colobodus Ag., Lepi- 

 dotus Ag. (Fig. 108). 



Fam. 3. Eugnathidae. Very similar to preceding ; elongated bodies ; 

 caudal fin homocercal or hemi-heterocercal ; Trias to Cretaceous. 

 Eugnathus Ag.. Ptycholepis Ag., Caturus Ag., Strobilodus Way. 



Fam. 4. Macrosemiidae. Macrosetnius Ag., Ophiopsis Ag., Prop- 

 terus Ag., Nofnr/ogus Ag. 



Fam. 5. Pholidophoridae. PholidopleuTus Broun. 



Fam. 6. Pycnodontidae. Body laterally compressed, high, oval ; 

 covered by rhomboidal scales, articulated together and strengthened 

 by a vertical ridge ; scales sometimes absent in the caudal region, rarely 

 absent altogether. Notochord persistent, without ossifications in its 

 sheath, but ribs, arches and spinous processes ossified. Caudal fin inter- 

 nally hemi-heterocercal ; fulcra absent ; pelvics small, anal and dorsal 

 Jong ; fulcra absent ; somactids of the unpaii'ed fins equal in number to 





Fig. lOS.^Lepidotiis minor, restored, one-fifth natural size, Purbeck Beds (from British 

 Museum Catalogue). 



the segmented dermotrichia ; opercular apparatus redviced, often only 

 one opercular bone present. Dentition of oval, crushing teeth. The 

 chondrocranium often well ossified. Infraclavicles absent. Jurassic, 

 Cretaceous, Eocene. Gyrodus Ag., Mestiirus Wagn., Mesodon Wagn. 

 (Fig. 109), P\jcnodus Ag.. etc. 



Fam. 7. Aspidorhynchidae. Very similar to preceding, but with 

 ring-shaped or complete and biconcave vertebrae (plevirocentra and hypo- 

 centra never distinct). Caudal fin homocercal ; snout elongated and 

 pointed ; scales rhomboidal, unequal ; lower jaw with movable pre- 

 mandibular ; fulcra weak. Lower Oolite to Upper Chalk. Aspidorhynchus 

 Ag., Belonostomus Ag. 



Fam. 8. Lepidosteidae. See p. 179. 



Order 4. Amioidei. 



Body covered with thin cycloid or rhombic scales, overlapping, 

 but not articulating, without ganoin. Caudal fin internally 

 heterocercal, externally symmetrical {hemi-heterocercal). Vertebral 

 column with either half -vertebrae or completely ossified amphi- 

 coelous vertebrae, or without vertebrae, ossification extending from 



