ACANTHOPTERYGII 679 



seas, Newfoundland, California, and Japan. It supplies im- 

 portant fisheries in France and Italy. The Tunnies are the only 

 fish known to be warin-blooded. 



Fam. 4. Trichiuridae. Praemaxillaries not protractile. 

 Vertebrae 32 to 160, without transverse processes; ribs sessile, 

 on the centra or on the haemal arches when these are present ; 

 epipleurals, if well developed, on the centra. Scales very small 

 or absent. Spinous portion of dorsal fin much longer than the 

 soft, the spines more or less feeble. Pectoral fins inserted low 

 down the sides. Pseudobranchiae present. 



The members of this family show a great variation in the 

 shape of the body, which, although always strongly compressed, 

 is not unlike that of a Mackerel in the more normal types, such 

 as Thyrsites and Ruvettus, whilst, through a chain of genera, it 

 generally assumes an extremely elongate form ; concurrently with 

 this elongation of the body, the dorsal fin loses its differentiation 

 into two portions, the ventrals become reduced and disappear, as 

 in the Scabbard- or Frost-Fish (Lepidopus caudatus), while the 

 caudal fin decreases in size, loses its fork-shape, and is finally 

 lost in Trichiurus, in which the body is ribbon-shaped and tapers 

 to a point. 



About 25 species are known, pelagic and widely distributed, 

 many descending to great depths. 



Principal living genera : Ruvettus, Thyrsites, Epinmda, Nesi- 

 archus, Nealotus, Promethichthys, Dicrotus, Gempylus, Aphanopus, 

 Lepidopus, Euoxymetopon, Benthodesmus, Eupleurogrammus, 

 Trichiurus. 



Eemains of several species referred to Thyrsites, Lepidopus, 

 and to the extinct genera Thyrsitocephalus, Hemithyrsites, and 

 Trichiurichthys, have been found in the Oligocene and Miocene of 

 Europe. 



Fam. 5. Histiophoridae. Praemaxillaries not protractile ; 

 snout produced into a spear-shaped rostrum ; a praedentary bone ; 

 teeth minute. Body elongate, covered with small or rudimentary 

 scales. Vertebrae 24 or 25, without transverse processes; ribs 

 sessile ; no epipleurals. One or two dorsal fins, without a 

 distinctly spinous portion. Pectoral fin low down the side. 

 Pseudobranchiae present. 



The Sail-Fishes are large oceanic fishes, endowed with great 

 strength and swiftness, occurring in the tropical and sub-tropical 



