HOLOSTEI 



501 



process may be completed within from 4 to 8 days. When 

 hatched the larvae are about 5 to 6 mm. long. They possess a 

 large yolk sac and a preoral sucker for attachment. The pectoral 

 fins are conspicuous structures before there is any trace of the 

 pelvic fins. 



FIG. 296. Amia and its nest. (From Bashforcl Dean.) 



The Amiidae, represented by Megalurus, 1 first appear in the 

 Upper Jurassic of Dorset, France, and Bavaria. In the Creta- 

 ceous period the family is represented by Amiopsis. Species of 

 Amia occur in the Eocene of Europe and North America. In 

 the former area the genus became extinct at the close of the 

 Lower Miocene period, but in the latter Amia calva still 

 survives. 



Fam. 6. Pachycormidae. Large-mouthed, predaceous Amioid 

 Fishes with a more or less prominent snout and a short dorsal 

 fin. Scales rhombic but thin, rounded behind, and overlapping, 

 sometimes absent. A single large jugular plate. 



In the earlier forms (e.g. Pachycormus, Lias) the snout is but 

 slightly produced, but in Hypsocormus (Upper Jurassic), and 



1 This genus also occurs in the Cretaceous of Brazil (Smith "Woodward, 

 A.M.X.H. (7) ix. 1902, p. 87. 



