140 Annals of the Carnegie Museum. 



resemblance is also to be noted between it and Pholidophorus. The 

 characters of the Alpine form were first recognized as constituting a 

 distinct genus by De-Alessandri^ in 1910. 



Turning now to the family Semionotida;, it is apparent that its 

 members represent a higher grade of structural organization than the 

 primitive sturgeon-like Catopterida?. A study of their characters 

 shows that the Semionotida? are fully developed Protospondyli; that 

 is to say, they belong clearly to that large group of "ganoid " fishes 

 which flourished chiefly during the Triassic and Jurassic periods, but 

 declined rapidly, and is represented at the present day only by two 

 freshwater genera, Lepidosteus and Aniia. From what ancient stock 

 the Semionotida; and other Protospondyli are descended, we do not 

 precisely know, but it may reasonably be inferred that the late Pale- 

 ozoic forerunners {AcenlropJwriis, etc.) of the higher suborder were 

 derived from a modified type of Chondrostean. Beyond this, when 

 we inquire as to the origin of the Chondrostei themselves, we find 

 but few facts for our enlightenment. Their origin is at least as ancient 

 as that of the fringe-finned "ganoids," but there is as yet no evidence 

 of a genetic connection between the Chondrostei and Crossopterygians. 

 Enough, however, has been ascertained to show that already in the 

 Trias and probably even earlier the divergence between Chondrosteans 

 and Protospondyli was strongly marked. 



Notwithstanding the close study which has been given to the re- 

 mains of the extinct fishes included in the families Catopteridce and 

 Semionotidcc, oui knowledge of their structural features is still in some 

 important respects deficient. t)r. A. Smith Woodward summarizes 

 the present state of our knowledge as to the first-named familj' as 

 follows: 



"The little that is known of Catopteriis and Dictyopyge, the two 

 genera of Catopteridcc, forms the subject of the opening pages of the 

 present volume. Much of this information is unsatisfactory, and 

 needs verification; but it may be asserted, with considerable probability 

 of correctness, that these fishes possess a Pala^oniscid head and shoulder- 

 girdle, while the tail is only hemi-heterocercal, and the single series of 

 supports in the dorsal and anal fins almost equals in number the 

 apposed dermal rays. Such being the case, here is an interesting 

 illustration of the common law, that the links between a lower and a 



1 De-Alessandri, G., "Studii sui pesci Triasici della Lombardia," Mem. Mus. 

 Civico Milano, 1910, Vol. VII, fasc. i. 



