GREGORY: FISH SKULLS 



299 



shorter and thicker, presumably implying a change from more delicate to larger food, the 

 •upper jaw has been shoved against the lateral ethmoids, which have become very thick, 

 even if cellular. Meanwhile with the subsidence of the nuchal fin crest, the crests of the 

 supraoccipitals and frontals have greatly diminished. The very peculiar downward and 

 backward turning of the cleithrum in Lampris has perhaps influenced the notable spreading 

 of the preopercular and opercular in the same general direction. 



On account of the retention of the orbitosphenoid bone and of the basic resemblance 

 of the cranium of Lampris and Velifer to the berycoid type, Tate Regan (1907(2, pp. 641, 

 642) infers that the order Allotriognathi has been derived from Cretaceous berycoids. 

 Jordan (1923, p. 166), on the other hand, places the Lampridae next to the Cretaceous 

 Semiophorus, a carangoid fish with a high dorsal fin extending on the forehead, — probably 

 a convergent resemblance. 



One of the most curiously specialized members of the order Allotriognathi is the deep- 

 water fish Stylephorus chordatus, the osteology of which has been described by Starks 



sphot 



J PP- hyom 



STYLOPHORUS 



Fig. 176. Stylophorus chordatus. After Regan. 



(1908a), and for which he established the suborder Atelaxia. ■ The very long body (Fig. 176) 

 is surmounted by a continuous dorsal fin and ends in an excessively long flagellum-like 

 tail. The large telescopic eyes are directed forward. The head as a whole is long with 

 the very long lower jaw projecting backward behind the gill region in a sharp elbow. One 

 would therefore expect to find a huge mouth, but on the contrary the mouth is quite small. 

 The relatively small premaxillae and maxillae both bear long dorsal processes. Tate Regan 

 (1929, p. 319) has described the action of this curious apparatus as follows: 



"By a downward movement of the lower jaw the upper is pulled right away from the 



