74 Anatomy and Classification of Scombroid Fishes. 



Family 2. Histiophoridse. 



Vertebrre 24 or 25 in number ; pelvic fins 1- to 3-rayed. 

 Neural and haemal spines expanded into strong overlapping 

 laminae ; ribs sessile. Scales present. Rostrum rounded in 

 transverse section ; teeth present ; a prsedeutary bone ; nasals 

 broadly attached to anterior edges of frontals ; maxillary of 

 nearly equal width throughout its length. 



Histiopftorus and Tctrapturus, perhaps dating back to the 

 Eocene. 



Family 3. Blochiidae. 



24 vertebrae. Pelvic fins absent. Neural and haimal spines 

 not expanded. Ribs apparently sessile. Body covered with 

 slightly imbricated, diamond-shaped, bony scutes ; two 

 longitudinal series of enlarged scutes on each side. 



Blochius longirostris, from the Upper Eocene of Monte 

 Bolca, attaining a length of one metre. 



Family 4. Xiphiidse. 



26 vertebrae. Pelvic fins absent. Neural and haemal 

 spines not expanded. Ribs inserted on transverse processes. 

 Scales absent in the adult. Rostrum depressed ; no teeth 

 in the adult; no praedentary bone; nasals extending back 

 on each side of the ethmoid and just reaching the frontals ; 

 maxillary formed of an expanded anterior and a rod-like 

 posterior portion. 



The adult Xiphias gladius differs considerably from 

 Blochius, but very young specimens clearly show its relation- 

 ship to the extinct genus. An example of nearly 200 mm. 

 in the British Museum is very similar to Blochius longirostris, 

 resembling it in the long slender jaws, the elongate body 

 with the greatest depth just behind the head, and the con- 

 tinuous dorsal fin. The body is covered with rough, non- 

 imbricated scales, wi;h 4 longitudinal series of enlarged 

 scales on each side, 2 corresponding in position to the lateral 

 series in B ochius and the others running at the base of the 

 dorsal and anal fins. 



The Lower Eocene Acestrus may belong to the Xiphiidae. 



