Actinopterijgii — Protospondyli. 



105 



tlie lower margin of the trunk. In several genera (e.g. Mesn- 

 flon, Microdoii., and Goelodus) the tail is destitute of scales. 

 These fishes range from the Lower Lias (JMesodon liassicus) 

 to the Upper Eocene {Fycnodus plafessus) with very little 

 modification. The fine series of examples of Gyrodns from 



Fig. 149. — Portions of Pycnodonts. a. transverse section of jaws, showing- the two 

 halves of the mandibular dentition opposing the vomerine teeth; li, dentition of 

 Miffodoii; '■, dentition of Cceiodus ; d, portion of vertebral column of Colodus, 

 showing persistent notochord (shaded), and tlie expanded bases of the arches; 

 e, the same of Pi/cnodun ; f, inner view of scales, showing mode of interlocking by 

 pegs and socliets, which are continued as longitudinal ribs. 



the Lithographic Stone of Bavaria, and of PalcPohaUstn-in 

 from the Hard Chalk of Moiint Lebanon, are particularly 

 worthy of attention. The armoured Coccodus and Xenopholis 

 from Mount Lebanon are also remarkable. None of these 

 fishes have vertebrae, but in the later genera the arches above 

 and below the notochord are often expanded to unite at the side 

 (Fig. 149). 



The Eugnathicla3 are the rhombic-scaled forerunners of the 

 modern Amia (Fig. 150), and range from the Upper Trias or 

 Rhsetic to the Chalk. They are predaceous fishes with a largo 



Wall-cases, 

 Nos. 12, 13, 

 Table-cases, 

 Nos. 43, 44. 



Fig. lul. — Eugnv.thv.s orlhostoMv.s, Ag. ; Lower Lias, Lyme Ecgis. 



