494 Evolution and Distribution of Fishes 



distribution two peculiarities of the living group Polypter- 

 idae, and of the now extinct related group Coelacanthidae 

 deserve mention. These all are, and seem to have been 

 small-mouthed fishes, that lived in muddy pools, and that 

 had rather imperfect oxydation. So migration was probab- 

 ly rather slow and limited in extent. Second, and doubtless 

 in correlation with the above habit, the air-bladder is a 

 large and usually ossified lobed structure that occurs often 

 fossilized in the coelacanths. 



As yet there is a wide gap in our knowledge of the 

 Crossopterygians. For none are known between the two 

 living genera 3.nd Macropoma of the Senonian and Turonian 

 Cretaceous rocks. The latter connects with Heptanema, 

 Coccodenna, Libys, Undina and Graphhirus of Jurassic 

 or late Triassic age. Reference has already been made to 

 the probable freshwater habitat of all of these except 

 possibly Macropoma, that may have become marine. The 

 above five genera, so far as now known, collectively occupied 

 a geographic area from S. E. England to Bavaria and N. 

 Italy, a region this that we have already indicated as the 

 likely evolutionary centre for many Jurassic and Upper 

 Triassic fishes. But Dipliirus from the Trias of Connecti- 

 cut and N. Jersey, that is in many structural points inter- 

 mediate between Undina of Kimmeridgean Liassic age, and 

 Graphhirus of Upper Keuper beds, again yields proof that 

 at that time central and south Europe were continuous with 

 Eastern America. 



The oldest genus Coelacanthiis includes a species from 

 the Upper Permian of Durham in England and Hesse in 

 Germany, several from the Coal Measures of England, 

 Scotland, S. Ireland and Ohio, U. S. also one (C. hiixleyi) 

 that is the oldest, smallest and most primitive from the 

 Calciferous rocks of S. Scotland. These occurrences would 

 seem to indicate connection, during Carboniferous times, 

 probably also in the Permian, from eastern N. America to 

 central Germany. 



The five still older divisions of the Crossopterygii ac- 

 cepted by Woodward, viz. the Onychodontidae, the Osteo- 

 lepidae, the Rhizodontidae, the Holoptychiidae and the 

 Tarrasiidae indicate collectively some extensive freshwater 



