HETEROMI 



Halosaurs, Notocanths 



Halosaurs. — These are a family of deep-sea fishes with elongate bodies and long tails 

 tapering to a point, without caudal fin and with the anal much elongated. The dorsal fin 

 is short, located on the middle of the back, above the short abdominal fins. The short 

 rostrum is pointed, projecting beyond the mouth, which is of fair size. According to 

 Boulenger (1910, p. 621) the air-bladder has no trace of an open duct (at least in Halo- 

 sauropsis, so that the fish is literally a physoclist, but primitive isospondyl characters are 

 the absence of spines in the fins, the cycloid scales, the abdominal ventrals, the parietal 

 bones separating the frontals. On the other hand, the mesocoracoid arch is absent (as 

 in Iniomi, Haplomi, Apodes, etc.). As to the otoliths, the sagitta of Halosaurus macrochir, 

 according to Frost (1926, p. 466), is of the elopine type, resembling that of Elops in certain 

 features and that of Megalops in others. 



According to Smith Woodward (1901, Pt. IV, p. 162; 1903, Pt. II, pp. 74-76), the 

 family is represented in the Upper Cretaceous of England, Westphalia and Mt. Lebanon 

 by the genus Enchelurus. In this form as described by Woodward (1903, p. 76) the cranial 



Enchelurus anglicus 

 Halosaurus oweni ^"^ 



Fig. 81. Enchelurus. .\fter Smith Woodward. Halosaurus oweni. 



vault (Fig. 81) is wide and fiat-roofed, the interorbital bridge elongate and narrow, with 

 distally forked ethmoid. The paired parietals and pterotics ("squamosals") form a trans- 

 verse row of four rather small fiat bones, which widely separate the supraoccipital from the 

 frontals. The premaxillae are relatively small, with a delicate rod-like extension behind, 

 bearing minute teeth. The maxilla is very large and closely similar to that of Halosaurus 

 in general shape. The gape of the mouth must have been small, and the relatively large 

 inferior Hmb of the preopercular extends forward to the articulation of the mandible. 

 The opercular is as deep as broad, rounded behind and quite smooth on its outer surface. 

 In the allied Upper Cretaceous Echidnacephalus the enlarged suborbital plates bear a well 

 developed slime canal (Woodward, 1901, p. 162). In the modern Halosaurus, according 



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