172 TBLEOSTBI. ACANTHOPTERYGII. 



apart. Body elongate and compressed, its greatest height opposite 

 origin of soft dorsal. Lower jaw slightly the longer, gape of mouth 

 rather narrow. Gill-openings cleft forwards to below anterior 

 edge of orbit. Fins dorsal spines of moderate strength, low, 

 with the interspinous membrane deeply cleft. Anterior portion 

 of second dorsal highest, equalling -| of body ; at a short distance 

 behind this fin are two rays placed close together and forming a 

 finlet ; they are rather elongate and reach the root of the caudal 

 fin. Pectoral short, ^ of the total length. Anal of the same form 

 but anteriorly lower than the soft dorsal, being \ of the height of 

 the body ; it has similarly a posterior finlet. Caudal deeply forked. 

 Scales on cheeks, upper edge of opercles, behind the eyes, and 

 over the body. Colour two longitudinal blue bands pass from 

 the eye, the upper to the dorsal finlet, and the lower to the centre 

 of the base of the caudal fin. 



Hob. Red Sea ; from the east coast of Africa, through tfie seas 

 of India, to the Malay Archipelago and beyond. This fish attains 

 several feet in length. 



5. Genus NAUCRATES, Cuv. 

 Syn. NauderuS) Cuv. & Val. (young). 



Branchiostegals seven. Body oblong, subcylindrical. Cleft of 

 mouth moderate. In the very young there is a spine at the angle 

 of the preopercle, which becomes absorbed as age advances. Villi- 

 form teeth in the jaws, vorner, and palatine bones. The first dorsal 

 fin, which is continuous in the young, becomes reduced to a few 

 spines in the adult ; the second dorsal and anal with many rays ; 

 no spurious fins ; in the young two preanal spines remote from 

 the soft fin, these become lost with age. Scales small ; lateral line 

 unarmed ; a keel on either side of the tail. Air-bladder present. 

 Pyloric appendages in moderate numbers. 



Geographical Distribution. These " pilot fishes" are spread through 

 all the seas of temperate and tropical regions. Most travellers in 

 sailing vessels have seen them as close attendants upon sharks, 

 leading them, as the sailors consider, to their prey. 



937. (1.) Naucrates ductor. (Fig. 59.) 



Gasterosteus ductor, Linn. Syst. Nat. i, p. 489 



Naucrates ductor, Day, Fish. India, p. 229, pi. li A, fig. 2 (see 



D. 3-6 \ 1/26-28. A. 0-2 \ 2/16-17. Csec. pyl. 12-15. Vert. 10/16. 

 Length of head 4 to 4i, height of body 4 to 4| in the total 

 length, %^-diameter 5 in length of head, li diam. from end 

 ot snout. ^ww-farst dorsal fin short, second dorsal highest an- 

 teriorly anal commences under the middle of the second dorsal. 

 Pectoral as long as the ventral, which reaches f of way to base of 



