162 PROCEEDINGS OF SOCIETIES. 



from whence it was forwarded, by the kindness of Professor Melville, to the Museum 

 of the Royal Dublin Society. It belongs to the sixth order of the second sub- 

 division of osseous fishes — namely, the Plectognathi, or fishes with soldered jaws. 

 In structure, this fish is intermediate between the osseous and cartilaginous fishes, 

 the skeleton, approaching the fibrous character of the former, still is slow to 

 ossify, especially the costal arches. The palate-bone is firmly united to the 

 skull, and, consequently, devoid of motion, in this respect differing from the 

 osseous, as also in having the maxillary and intermaxillary bones fused toge- 

 ther, so as to form one piece, their union being marked by a mere groove. The 

 gill rays are completely covered by the opercula, which latter form a perpendicular 



slit of about one inch long. The dental formula is — ; , the teeth being set in 



a semi-osseous or muco-cartilaginous nidus, well adapted to the habits of the 

 creature, as feeding for the most part on the polypi of coral reefs, the teeth are 

 formed for browzing, and, in all probability, grow much after the manner of 

 rodents — that is, from behind forwards. 



" This specimen, indeed I may say the entire genus, though provided with pelvic 

 bones, still are destitute of ventral fins. It is true they are furnished with a few 

 short spines, in or about the situation of the pelvis, which may be considered as 

 the rudiments of these organs. 



" As this fish lives upon food not requiring great complexity for its digestion, we 

 accordingly find that its internal organization is not elaborate. The stomach is 

 capacious, but the intestinal canal, though of considerable size, is destitute of 

 coeca. It is provided with a swim-bladder, to enable it to remain near the surface 

 of the water whilst engaged in seeking its food among the coral reefs, where it loves 

 to dwell. It possesses two sets of scales, those near the head tubercular or warty — 

 hence, scleroderme ; secondly, those on the centre of the body, like the scales of 

 the osseous fishes, but that in these fishes they do not overlap as in the latter. 



"It is named "File-fish," in consequence of the first dorsal spine being covered, 

 on its anterior edge, with rough granular projections ; and the term " Balistes" 

 has reference to another peculiarity in the structure of that spine and the one im- 

 mediately adjoining, which peculiarity Salviani was the first to discover — viz., that 

 the bones, or rays, of the first dorsal fin are so contrived as to act in concert, with 

 considerable force, in suddenly elevating the fin at the pleasure of the animal ; 

 though the foremost, or largest, be pressed ever so hard, it will not stir ; but, if 

 the last, or least, ray of all be pressed but very slightly, the other two immediately 

 fall down with it, as a cross-bow is let off by pulling down the trigger. For this 

 reason the fish is called, at Rome, *• pesce balestra. , 



" For the following measurements he was indebted to his friend, Mr. E. P. 

 Wright: — Length of specimen, from snout to extreme end of caudal fin, 

 sixteen inches; depth seven one-fourth inches, being something less that one- 

 half the length ; the first spine of the dorsal was unfortunately broken on 

 its capture. The head declines gradually from the first dorsal fin, with slight 

 depression over the eyes ; width of mouth, from centre of jaws, six-eighths of an inch ; 

 number of teeth, sixteen, four on each side of both jaws, bent inwards ; eye small ; 

 orbit six-eighths of an inch in diameter ; from eye to eye, across forehead, one 

 five-eighth inches ; nostrils, situated close to the eye, between it and the upper 

 jaw, consist of two small perforations. The fin ray formula is as follows : — 

 1st, D 8 ; 2nd, D 28 ; P 14 ; A 26 ; C 14. 



" All the rays are slightly free at apex. There is a space of nearly one inch 

 between end of anal and beginning of caudal ray ; the longest ray of the latter is 

 four inches, and the shortest two. The first ray of the dorsal fin is in a vertical line 

 over the branchial orifice ; the second dorsal and anal both begin in a vertical line. 

 A rough skin, covered with scales, takes the place of the ventral ray. These mea- 

 surements accord pretty nearly to those given by Yarrell, with the exception of the 

 pectoral fin, which in his ray formula has fifteen rays ; but both his figure and 

 the coloured engraving in the Naturalists' Library (plate 21, vol. ii., of the British 

 Fishes, by Dr. Hamilton), represent the caudal fin as wedge shaped ; whereas in 

 this specimen, as will be seen from the above measurements, it forms the arc of a 

 large circle. Its colour is brownish gray." 



