GREGORY: FISH SKULLS 



363 



Trachinus. — The outstanding feature of the skull (Fig. 243) (Nos. 273, 274, Brit. 

 Mus. Nat. Hist.) is the very large spine which projects straight backward from the dorsal 

 part of the opercular. This spine is said to be poisonous. The skull top (Fig. 245) is 

 rounded, with no crests, the surface being covered with a close-set pattern of many tubules 

 and openings, possibly derived by branching of the lateral line canals. There is a row of 

 small denticulate projections above the orbit and three of them on the lateral ethmoid. 



pop 'top 



Trachinus draco 



Fig. 243. Trachinus. 



The general appearance is that of a small percoid which has begun to parallel the scorpsenoids 

 in a few features. The hyomandibular shows the beginning of a lateral process starting 

 from the upper end of its preopercular crest, which process is greatly emphasized in the 

 uranoscopoids. The preopercular offers nothing conspicuous; it differs widely from that of 

 Trichodon (see p. 370), as does the lacrymal. The mouth is directed somewhat upward. 

 Taken as a whole the skull could well be the starting-point for the specializations of the 

 Uranoscopidae but has not acquired their diagnostic characters. It is surely widely removed 

 from Trichodon. The pectoral girdle, including the actinosts, also differs widely from that 

 of Trichodon. On the whole Trachinus is nearer to Uranoscopus than to Notothenia. 

 Its otolith, as described by Frost (1928a, p. 454), could be conceivably derived from the 

 Parapercis type and give rise to the Uranoscopus type. 



Percophis. — A skull of Percophis brasilianus (No. 283, Brit. Mus. Nat. Hist.) represents 

 a fairly large-mouthed predaceous type, long and low with a projecting mandibular tip, 

 the mouth opening obliquely upward. The jaws are modefately protractile. Tate Regan 

 (1913, p. 140), who refers Percophis to the Percophiidae, says that the skull is "much as in 

 Trachinus, but more depressed, with the exoccipital united behind the supraoccipital, 

 forming a roof for the foramen magnum." The pectoral girdle, including the actinosts, is of 

 modified percoid type, in some features similar to that of Pinguipes (Fig. 237). 



Dactylagnus. — In this genus of the family Dactyloscopidae the skull (Fig. 244) as 

 described and figured by Starks (1923) shows an early stage in the line leading toward 

 Uranoscopus but also retains traces of more primitive percomorph characters. Thus the 



