140 



PALEONTOLOGY 



are of moderate size ; all the species are sub-liomocercal * and 

 notochordal (fig. 53). The dorsal, d, is opposite the ventral, r. 

 One species of Caturus {C. BucMandi) is from the lias ; but 

 the majority, like G.furcatus, are from the lithographic slates 

 of Solenhofen. The most recent known species (C. similis) is 

 from the chalk of Kent. 



Pachycormus, Sawostomus, Sauropsis, Thryssonotus, and 

 Euynathus, are liassic genera of the present family. It is 

 deemed by some Palaeontologists to be represented at the 

 present day by the North American genus Lepidostcus ; but 

 in this fish the notochord is converted into bony vertebral 

 bodies, united by ball-and-socket joints, and the tail is hetero- 

 cercal. 



Family VIII. — Pycnodontes. 



The name of this group of ganoid fishes refers to the blunt 

 rounded form of the greater proportion of the teeth, especially 

 those attached to the palate and hind alveolar part of the 



lower jaw : the few 

 anterior teeth are 

 small and sub-prehen- 

 sile ; but the whole 

 dentition bespeaks 

 fishes adapted to feed 

 on small testaceous 

 and crustaccous ani- 

 mals. In the modern 

 Fig. 54. " Sea Breams " (Spa- 



Platysomus giblosus (zechstein of Mansfield). roids) with all analo- 

 gous dentition, the two premaxillaries oppose the two pre- 

 mandibulars, but in the extinct Pycnodonts the vomer, as in 

 Anarhichas, opposes its pavement of teeth to that of the two 



* By tins term is meant a symmetrical shape of the tail fin, with an unsym 

 metrical developmenl of the supporting Bpines, the terminal vertebrae inclining 



to the upper lobe. 



