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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



and is not concerned with the relationships of that fish with other scombroid fishes. This 

 subject is dealt with by Starks (1910) in a paper that is illustrated with excellent views 

 (Fig. 189) of the dorsal aspect of the crania of Scomber, Scomberomorus and Sarda, while 

 the osteology of these and related genera are described in the text. 



In a diagram illustrating the inferred relationship of the various genera, as based on 

 the data recorded in this paper, Starks puts the true mackerel (Scomber) on or near the 

 trunk of the tree; the Spanish mackerel (Scomberomorus) and the tunnies (Thunnus, Auxis 

 (Fig. 190), Gymnosarda) belong on opposite forks, while Sarda, which combines the cranial 

 features of the two forks, stands between them. It will readily be seen that the arrangement 

 of the crests on the cranial roof of Scomber (Fig. 189) is basically the same as in the normal 



— ^ Scomber 



Fig. 188. Scomber. After Allis. 



percoid genera, in which the skull is narrow in front; while that of Scomberomorus (Fig. 

 1895) differs in the broadening of the interorbital bridge and prefrontal area so that the 

 skull top appears more or less oblong. At the same time the anterior end of the ethmoid has 

 grown forward to form a concave facet for the blunt ascending process of the premaxillse, 

 the nasals are stout and tend to face laterally. The occipital crest, although low, extends 

 forward over the frontals to the ethmoid, while parallel and continuous crests on either side 

 run forward from the epiotic over the parietals on to the frontals. The skull top of Sarda 

 (Fig. 189C) appears to me to have been derived directly from some ancestral form that much 

 resembled that of Scomberomorus, by the widening and shortening of the whole skull, by the 

 spreading laterally of the concave ethmoid facet for the premaxillae, by the divergence of the 

 epiotic parietal crests. The opisthotics widen transversely and the posterior pterotic 

 processes become elongate. 



In the tunny (Thunnus) the skull becomes very wide, in accordance with the robustness 

 of the smooth rotund body. Figures 191-193 bring out well the curious features of this 



