342 Evolution and Distribution of Fishes 



age," and if B. sioceti from the " Rolling Downs" of Aus- 

 tralia undoubtedly is found with marine remains, such would 

 suggest that both genera may have become marine before 

 dying out. But added and exact information is needed. 



Lepidosteus, the sole surviving genus of the family 

 Lepidosteidae is and has been purely freshwater in habitat, 

 as the descriptions of Leidy, Cope and others indicate. In 

 the transition Bridger beds that usher in the Eocene forma- 

 tion of Western America, remains of several species have 

 been secured. In the Upper Eocene and in Miocene beds 

 of England, Belgium and West Germany, various rather 

 scant but determinable traces have been found. With com- 

 plete separation of the land areas of Europe and N. Ameri- 

 ca, the genus persisted in the latter region, where it is now 

 represented by the two large, voracious, and powerful 

 species of Gar-pike, L. platysomus that is abundant in most 

 rivers and lakes of the United States, and L. viridis that 

 is native to the Southern States, also Cuba and Mexico. 



The remaining groups of the "ganoid" fishes that are 

 now usually united into a large sub-order the Isospondyli 

 can next be examined. The term is applied, and the series 

 Is so distinguished, because the vertebral centra from now 

 onward in the ascending scale of evolution, become through- 

 out the entire length of the notochord definite osseous rings 

 of tissue that encircle it, and that show equal anterior and 

 posterior faces to the vertebrae, so that these are amphi- 

 coeJoiis. 



In the more primitive families of the Sub-order, many 

 typical characters of the Aetheospondyli still persist, apart 

 from the ganoid scales, but as with the Aetheospondyli so 

 with the Isospondyli, the highest representatives pass al- 

 most insensibly into the most ancient of the Teleosteans. 

 The three included families are the Pholidophorldae, the 

 Oligopleuridae, and the Leptolepidae. 



The first of these is made up of at least seven genera, 

 Thoracopteriis, PhoUdopleiiriis, Peltopleurus^ PhoUdopho- 

 rus, Archaeomene, Pleuropholis, and Ceramurus. In the 

 Upper Triassic beds of Europe, Asia, Africa and Australia, 

 a remarkable admixture of protospondylic and isospondylic 

 ganoids is met with. So true is this that side by side on 



