220 Evolution and Distribution of Fishes 



of the Triassic, upward to the Purbeck or mid-upper beds 

 of the Jurassic. These again led to the Leptolepidae, and 

 in regard to the last Woodward {i6g :lntrod. p. XIX) 

 says: "as already observed by Agassiz, the genus Pholido- 

 phorus exhibits a very close resemblance to Leptolepis in 

 general aspect, the osteology of the head being remarkably 

 similar, vertebral rings being tolerably well ossified, the fin- 

 fulcra very small and usually lost, while the scales are often 

 extremely thin and deeply overlapping though for the most 

 part united by a peg-and-socket articulation; and it is note- 

 worthy that no identifications of splenial and coronoid 

 elements have hitherto been discovered in the jaw." 



In the Leptolepidae the fin-fulca have been absorbed, 

 the bones of the mandible have condensed to two elements, 

 the spiral intestinal valve has nearly or wholly been absorb- 

 ed, intermuscular bones — absent in the last — gradually 

 developed in OUgopleurus and are large in Leptolepis, 

 while a faint trace of ganoine often persists on the exposed 

 part of each scale. The genus Leptolepis extends from the 

 Lias upward through the Stonesfield Slates of England 

 and the Wianamatta of Australia, on through the Kim- 

 meridge and Purbeck periods to the Cretalceous. The 

 division then seems gradually to have broken up into several 

 groups, the Diplomystidae, Clupeidae, Elopidae, and Albu- 

 lidae, most of which passed seaward during late Cretaceous 

 or early Eocene time, though some persisted in their old 

 environment. Even now however, most of them are shore 

 dwellers, while the shad and allied types still return to 

 brakish or freshwater in the spawning season. A further 

 study of these is given on p. 348. 



The flora of the Cretaceous period is as suggestive in 

 character as are the fish, the amphibian and the reptilian 

 faunas. For it is from the base of the system upward, that 

 an increasingly extensive array of angiospermic flowering 

 plants appears. By a set of combined characters, that it 

 would be out of place to discuss here, these in time became 

 dominant over the gymnosperms and fern allies, until by 

 the Eocene period they were highly conspicuous. Coeval 

 with them appeared those types of insect, like the bees, 



