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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



ChjEtodontoidei (Butterfly-fishes, Angel-fishes, etc.) 



The butterfly-fishes (chaetodonts and their allies) show some general resemblances to 

 the pomacentrids but they were regarded by Boulenger (1910, p. 667) as "closely allied to 

 and evidently derived from the more generalized types of the Scorpididae." Tate Regan 

 (1913a, p. 128) refers them to his rather comprehensive group Perciformes, following the 

 Monodactylidae, Scorpididae, Ephippidae, Drepanidae and related side-shoots. Starks in 

 his valuable work on "Bones of the Ethmoid Region of the Fish Skull" {\926a, pp. 272- 

 275) emphasizes the close agreement of the chaetodonts with the Drepanidae as showing 

 the very exceptional junction of the opposite prefrontals (lateral ethmoids) in front of the 

 main plate of the mesethmoid. 



An examination of skulls of Scorpis, Psettus, Platax, in comparison with those of the 

 ephippids and chaetodonts, indicates that Boulenger's conclusion as quoted above is correct, 



Fig. 150. Scorpis sp. 



at least in that the skull of Scorpis (Fig. 150) forms a structural base for the chaetodont 

 series and connects it with some deep-bodied primitive percoid with twenty-four vertebrae 

 and pelvic fins with one spine and five soft rays. As shown in Figure 150 the skull of 

 Scorpis georgianus (No. 202, Brit. Mus. Nat. Hist.) is of primitive percoid type, hardly 

 any of the elements showing conspicuous peculiarities. Perhaps in response to the deepen- 

 ing and compression of the body, however, the opposite lateral ethmoids are extended 

 transversely and meet in a broad suture above the parasphenoid, forming a strong anterior 

 pillar of the skull; they are pierced by the olfactory foramina in the normal way. The 

 dorsal crest suggests that of the chaetodontoid fishes since its muscle area does not extend 



