FISH FAUNA. 65 



G-LTPHIDODON POLYACANTHUS, sp. 710V. 

 B.VI. D. 14/13. A. 2/14. V. 1/5. P. 16— 18. C. 17. L. 1. 27. L. tr.4/10. 



The length of the head is from four and a half to four and three-fourths, 

 the height of the body rather less than three in the total length. The 

 diameter of the eye is from two and four-fifths to three and two-fifths in 

 the length of the head, equal to or in large examples rather less than 

 that of the snout, and equal to or five-sixths of the interorbital space, which 

 is slightly convex. The greatest depth of the preorbital is almost equal to 

 the diameter of the eye. The maxilla does not nearly reach the anterior 

 margin of the orbit. Fins. — The dorsal spines are strong and moderaiely 

 high, the middle ones rather higher than the posterior, about three-fifths 

 of the length of the head, and two-thirds of that of the middle dorsal rays, 

 which are one-half longer than the base of the soft portion of the fin, which 

 is rather pointed : the second anal spine is very strong, slightly curved back- 

 wards, and equal to or but little more than the longest dorsal spine ; the 

 soft portion of the fin is rounded, the middle rays being barely longer than 

 the base : the first ventral ray is produced into a filament, which reaches to 

 the middle of the anal fin, and is one-third longer than the head : the pectoral 

 fin is well developed, about one-sixth longer than the same : the caudal fin is 

 forked with the lobes, more or less rounded in adults, but acutely pointed in 

 young and half-grown examples, the upper much longer than the lower, and 

 from one-seventh to one-third longer than the head. The lateral line ceases 

 beneath the middle of the soft dorsal. Colors. — Varying with age ; adult 

 specimens are dull brown without any trace of markings whatever ; the soft 

 dorsal, anal, caudal, and ventral fins black, the pectorals yellowish-brown ; 

 half-grown examples are pale violet-brown shading into yellowish-brown on 

 the lower third of the body ; cheeks, opercles, and preorbitals with numerous 

 round spots and short streaks of sky-blue ; occiput and scales on the anterior 

 part of the back above the pectoral fins with minute dots of the same color ; 

 a row of similar spots from the snout, where it joins the corresponding one 

 of the opposite side, through the upper part of the eye to the dorsal ocellus, 

 which is black, surrounded by a circle of blue spots, and lies beneath the 

 tenth to thirteenth dorsal spines ; a similar but smaller spot on the last two 

 rays and the anterior part of the pedicle ; vertical fins of the same shade 

 as the body ; ventral s and pectorals yellow or grey ; a black spot at the base 

 of the lateral line and another in the axil of the pectoral. In the young the 

 ground color of both body and fins is pale buff, and the arrangement of the 

 ornamental markings is similar to that of the half-grown, but the spots are 

 much more accentuated, and the naso-dorsal line is composed of confluent 

 blue black-edged spots. 



In the series of ten examples received through Mr. Saunders, there are 

 almost endless modifications of the colors above given, which however appear 

 to be typical of the three stages of growth mentioned, and I am satisfied that 

 they are the various ages of the same fish, while the difference in coloration 

 is to my mind easily accounted for thus : The young frequent shallow rock- 

 pools with a sandy or coralline bottom, exposed to the full light of the sun, 

 and naturally assume a tint similar to their surroundings, but as they increase 

 in size they gradually retire to the larger and deeper pools near the outer 

 edge of the reefs, which are only exposed at low spring tides, and whose sides 

 are covered with a rank growth of seaweeds, and here they take on the more 

 sober livery of the adult fish. 



Both in the inconstancy and the pattern of its coloration the present 

 species bears a striking resemblance to Glyphidodon broicnriggii but here 

 again I am confronted by the unbroken constancy through a most typical 



