286 Evolution and Distribution of Fishes 



After formation of the Coal Measure beds, some wide- 

 spread agency evidently blotted out the elasmobranchs 

 wholesale, for only five genera — and these all freshwater — 

 Acanthodes, Pleuracanthtis, Diplodiis, Janassa, and Wod- 

 nika survived, though in greatly reduced number of 

 species. But from the accounts of Fritsch, Kner, and 

 Sauvage, the individuals of some species were occasionally 

 very abundant. The remarkable feature however is that 

 the destruction of fish-life was more pronounced on the 

 sea than on land; so that of the true elasmobranchs named 

 above the first four genera alone survived, while of the 

 Cestracionts JVodnika is alone known to us. All five of 

 these seem to have been wholly, or as with Diplodus in most 

 of its species, mainly freshwater. 



The question may well be asked then: Did a complete 

 obliteration of marine, and largely also of freshwater, 

 elasmobranch fish-life occur toward the close of the Car- 

 boniferous or in early Permian time? Such seems to have 

 been true, so far as present exact records lead us, while 

 as stated below, they alone persisted in inland lakes till 

 later Jurassic times when a gradual reinvasion of the 

 sea took place. The immigrant types then reintroduced 

 have persisted in their more or less direct descendants, to 

 our own day. This temporary destruction — almost to the 

 disappearing point — of a large group like the elasmo- 

 branchs, that had not only multiplied extensively in fresh- 

 water, but had spread thence into the sea, is one of the 

 most arresting facts in natural history. For the slow and 

 very gradual reappearance of them, doubtless by fresh 

 evolution from the few genera spared alive, in Jurassic 

 and specially in Cretaceous strata, suggests that some 

 sudden, cataclysmic, and wide physical change took place, 

 that was most felt over the ocean, somewhat less over 

 freshwater and land areas. 



A paper directly bearing on the Permian elasmobranch 

 fauna is that of M. E. Roche (2/0:9:78; not v.20 as 

 quoted by Sauvage). In this he distinguishes three hori- 

 zons at the base of the Permian bituminous schists of 

 Autun. All are characterized by definite species of fish. 

 In addition to typical freshwater crossopterygians and 



