Distribution of Primitive Fishes 495 



systems, that other groups of equally ancient fishes, which 

 are reviewed below, seem fully to confirm. If we neglect 

 the little known Onychodus, it can be said that most of the 

 Osteolepidae are only recorded from Britain, but species 

 of Glyptopomus have been found from Belgium and Scot- 

 land, west to the Catskill group on the Susquehanna of N. 

 America. The Rhizodontidae, that have a vertical per- 

 sistence very nearly like that of the last, viz. from the 

 Lower Old Red to the Upper Coal Measures, are known 

 from an even wider area. Thus Strepsodus, Rhizodus, and 

 Rhizodopsis collectively extend from Galicia through 

 Britain, to Ohio, Nova Scotia, and doubtfully to Spitz- 

 bergen. Cricodus, Eiisthenopteron, and Holoptychius — 

 mainly from Upper Devonian beds — extend from W. Rus- 

 sia through Belgium and Scotland to E. Canada, N. York 

 and Pennsylvania. 



The Dipneusti, like the Crossopterygii, can be traced 

 backward from such living genera as Protopterus, Lepido- 

 siren, and Neoceratodus, through successively older and 

 wholly freshwater strata, to rocks of Lower Old Red age. 

 Regarding the two first of these as indicating an Afro- 

 American Cretaceous-Eocene continent, nothing need be 

 added to what has already been set forth. The existing 

 Neoceratodus of Queensland connects fairly well, though 

 by a wide geologic gap, with the species of Ceratodus that 

 once peopled the rivers and pools of lower Triassic to mid 

 Jurassic age. And like not a few groups already treated of, 

 they seem to have been most abundant at that time In 

 central Europe, but extended eastward to Upper Triassic 

 beds of India and of Australia, as well as southward to the 

 Karoo beds of Africa. If C. guentheri also is correctly 

 recorded and interpreted {30^: j6) this species reached 

 Colorado in Upper Jurassic time. Here then is added 

 proof that N. America, central and S. Europe, India, S. 

 Africa, and — by the genus Gosfordia — East Australia were 

 more or less in organic relation during Triassic-Jurassic 

 time. 



A gap In the history of the group again exists from the 

 Triassic to the Lower Permian, but from the latter period 

 Sagenodus, Ctenodiis, Phaneropleuron, and Dipterus, carry 



