GREGORY: FISH SKULLS 237 



The maxilla bears the primitive two supramaxillse, while its proximal process, articu- 

 lating with the vomer, is overlapped dorsally as usual by a strong process of the palatine. 

 The most conspicuous feature of the side view is the very prominent spine at the postero- 

 inferior angle of the strongly ridged preopercular, a feature not seen in fishes below the 

 acanthopt level. The vertically extended opercular also bears a prominent strong spine, 

 below which are sharp serrations. There is a "ball and socket" joint between the dorsal 

 rim of the lacrymal and the lower border of the dermal prefrontal (Fig. 1125). 



The cranial roof (Fig. 112) is very dense and solid. Just above the hyomandibular 

 facet it bears a prominent fossa for the dilatator operculi muscles. In the top view (Fig. 

 112C) the small epiotic and supraoccipitals are depressed beneath the prominent plaited 

 surface of the broad frontals, which are now the dominant elements of the cranial roof. 

 Anteriorly there is a large deep median groove above the mesethmoid, flanked by conspicu- 

 ous processes formed by the nasals and frontals and serving for the reception of the long 

 ascending processes of the maxillae. The circumorbital bones number six, as is usually the 

 case, especially in acanthopts, counting the so-called dermosphenotic as the sixth. 



Starks has shown (19086, p. 613) that in Holocentrus ascensionis the air-bladder sends 

 forward on each side a diverticulum, the inner membrane of which forms a loose tympanum 

 covering the posterior opening of a tube-like prominence of the otolith chamber. The side 

 of this chamber is formed chiefly by the backwardly prolonged prootic, assisted by the ex- 

 occipital and basioccipital. In the species Holocentrus {Adioryx) suborbitalis this connec- 

 tion between the air-bladder and the otolith chamber is absent (p. 614). The otoliths of 

 the Berycoidei, as described by Frost (1927a, pp. 440, 444), show a wide range in form from 

 the primitive "Berycoid"- type of Polymixia to the aberrant form in Myripristis. In the 

 Holocentridae the general form of the sagitta is similar to that of Elops, but the sulcus is 

 distinctly percoid in character and the posterior rim is modified. Mr. Frost concludes 

 (p. 440) that these facts tend to confirm Mr. Tate Regan's position that while the berycoids 

 approach the percoids in general structure, they also retain many features which indicate 

 their relationship to primitive clupeoids. 



In conclusion, the ancestry of the berycoids and consequently of the entire percomorph 

 series is apparently to be looked for in the neighborhood of the Cretaceous isospondyl 

 Ctenothrissa, as held by Regan (1929). Assuredly this form approaches the short-bodied 

 acanthopt type more closely than do any known scopeloids, which are typically long-bodied 

 and more or less advanced on the roads leading to Haplomi, Microcyprini, etc., which are 

 at most pseudo-acanthopts rather than true pre-percomorphs. 



Percoidei (Bass, Perch, Snappers, Sparids, Cichlids, Wrasses, etc.) 

 "The large and varied order Percomorphi," writes Tate Regan (1913a, p. Ill) "occupies 

 a central position among the Teleostean fishes. On the one hand it appears to be derived 

 from the Berycomorphi, and on the other it seems to have given rise to a number of special- 

 ized offshoots, which may be regarded as ordinally distinct: Scleroparei, Heterosomata, 

 Plectognathi, Discocephali, Xenopterygii, Pediculati, Symbranchii, and Opisthomi." He 

 then proceeds to define the order Percomorphi as follows: 



"Symmetrical acanthopterous physoclists with normal dorsal fin, pelvic fins never 

 more than 6-rayed, subabdominal, thoracic, jugular, or mental in position, the pelvic bones 

 typically attached to the cleithra; principal caudal rays not more than 17. No orbito- 



