Fishes of the Western North Atlantic 



1 1 



nares of the Dipnoi are homologous with those of the tetrapod vertebrates. At any rate, 

 they are not used in respiration. 



Although objection may be raised to the use of Sarcopterygii when older names 

 are available, this name does not carry with it any evolutionary implication that may 

 not be warranted; and furthermore, it has never been employed in more than one sense, 

 hence it is accepted here. This Subclass need not concern us further, for the Dipnoi are 

 strictly confined to fresh water while living representatives of the coelacanths have been 

 taken only off the southeastern coast of Africa and near Madagascar. 



Actinopterygii has been chosen here as a Subclass name to represent the bony 

 fishes that remain after subtracting the Sarcopterygii, a course which accords with the 

 weight of contemporary opinion. An alternative scheme, proposed by Regan {6g: 458; 

 'JI [1937]: 312) and adopted by Norman (55: 376-377), would distribute them in two 

 Subclasses: Palaeopterygii for acipenserids, polyodontids, and polypteroids; and Neop- 

 terygii for the remaining groups. But this seems an unnatural arrangement; although 

 the polypteroids and acipenserids are similar in that the number of fin rays is greater 

 than the number of their basal skeletal supports and because there is an unmistakable 

 spiral valve in the intestine, the polypteroids differ widely from the acipenserids in the 

 nature of both caudal fin^i and dorsal fin, in the segmentally constricted notochord, 

 and in the presence of a pair of bony gular plates between the branches of the lower 

 jaw. Indeed, the polypteroids differ so widely from all other living bony fishes that 

 Bertin and Arambourg's separate Subclass for them, Brachyopterygii (jJ: 198 i, 2500), 

 may represent a step forward in attempts to present more accurately the affinities of 

 the various groups of bony fishes. 



Subclass ACTING PTERTGIP-' 

 Ray-finned Fishes 



Characters of Living Members. The skull in its early stages is a primitive cartilaginous 

 cranium that is replaced during development by bone in varying degrees in different 

 groups; in most of the living bony fishes it is completely ossified in adults. Its outer 

 surface is invested with a covering sheath in an intricate pattern of so-called dermal or 

 membrane bones that develop as new structures "in the membranes of certain regions 

 of the skull" and that appear to represent such modified scales; thus the entire skull 

 is "so welded together to form a compact whole that in the adult fish it is often im- 

 possible to decide as to which category a particular element belongs" {55: 161). 



Generally the upper jaw includes paired premaxillary and maxillary bones ;'^ the 

 premaxillaries, supplemented in many cases by the maxillaries, form the upper region 



31. Symmetrical in the polypteroids, with the posterior part of the vertebral column continuing the axis of the body; 

 strongly asymmetrical in the acipenserids and polyodontids, with the posterior part of the vertebral column bent 

 upward (heterocercal). 



32. Including the polypteroids. 



33. Premaxillaries are lacking among acipenserids (sturgeons) and polyodontids (paddlefishes) {32: fig. 20); in Bathy- 

 saurus of the Iniomi and in Gigantura maxillaries are lacking; both premaxillaries and maxillaries are lacking 



