GREGORY: FISH SKULLS 157 



premaxillae not quite excluding the rod-like maxillae from the corners of the mouth. The 

 premaxillae have short ascending processes and the conditions represent the initial phase 

 in the protrusility of the premaxillae. The suspensorium and opercular series present little 

 that is unusual. The orbitosphenoids are absent (see also Starks, 1908f, p. 414). The 

 dermal mesethmoid as seen from above is circular, much as in Fu7idulus. 



Thus the leading characters of Galaxias appear to indicate its relationships with the 

 Haplomi and their relatives. Tate Regan, however, in his revised Classification of the 

 Teleostean Fishes (1909a, p. 82) referred the Haplochitonidae and the Galaxiidae to the 

 Isospondyli in the following passage (p. 82): 



"In some external characters Retropinna is intermediate between Osmerus and Proto- 

 troctes. Retropinna, Salanx, and Microstoma are Argentinidae which have no mesocoracoid. 

 The Argentinidae, Haplochitonidae and Galaxiidae are extremely similar in osteology, 

 dentition, and in the absence of oviducts, and are undoubtedly closely related. 



"It is possible to maintain the order Isospondyli, with the addition of the Haplo- 

 chitonidae and Galaxiidae, by taking into consideration the mouth structure, the maxillary 

 entering the gape to a greater or less extent (almost excluded in the Haplochitonidae) and 

 the unpaired ethmoid. As thus defined, the Haplomi, Iniomi, and Microcyprini are 

 excluded." Here then we have added evidence of the shadowy nature of the boundaries 

 between the Isospondyli, Iniomi, Haplomi and Microcyprini, as long ago noted by Smith 

 Woodward and others. 



Stomiatoidea 



Jlepocephalus is placed by Tate Regan next to the Ctenothrissidae among the clupeoids 

 and it shares with that assemblage the diagnostic character of two supramaxillaries. With 

 the salmons it shares the secondary development of the cartilaginous chondrocranium. 

 It illustrates an early stage of the effect of abyssal life on a branch of the clupeoid stock 

 and might be a structural ancestor of the stomiatoids, at least in many respects (Fig. 51). 



In Maurolicus and Ichthyoccus, which are generally referred to the Gonostomidae, the 

 photophores are arranged much as in the short-bodied Sternoptychidae, but the body is of 

 moderate length. Maurolicus (Fig. 52C) in fact appears to be the descendant of an ancient 

 common stock which diverged, on the one hand, into such excessively deep-bodied forms 

 as the Sternoptychidae and, on the other, into the long-bodied Astronesthidae, Chaulio- 

 dontidae and Stomiatidae. According to Tate Regan (1923^, p. 613) the Gonostomatidae 

 are near the Elopidae. "Comparing Photichthys with Flops," he writes, "I find a striking 

 agreement in the head-skeleton, the general form of the skull and the relations of the 

 bones being almost exactly the same. In Photichthys the orbitosphenoid appears to be 

 absent and the posterior temporal fossae are somewhat smaller than in Elops, but there are 

 no other differences of importance." 



Smith Woodward notes (1908, p. 138) that in the extinct Tomognathus mordax from 

 the English Chalk the skull and dentition are in some respects "suggestive of those of the 

 Stomiatidae and their allies, which exist in the deep sea." This form, like Astronesthes, 

 has a quite short head with the orbit very large and far forward; the jaws are fairly short 

 with very strong pointed teeth in front. 



In the narrow and deep-bodied Sternoptychidae (Fig. 52) the suspensorium is inclined 

 forward progressively as we pass from Argyropelecus to Sternoptyx to such a degree that the 

 preoperculars are finally lateral to the postero-external part of the huge upturned eyes and 



