Zoology.} NATURAL HISTORY OF VICTORIA. [Fishes. 



Plate 143. 



MONACANTHUS PERONII (Hollard). 



Peron's Leatherjacket. 



[Genus MONACANTHUS (Cuv.) + Aldterius (Cuv.). (Sub-kingdom Vertebrate. 

 Class Pisces. Sub-class Telostei. Order Plectognathi. Family Scleroderma) 



Gen. Char. — Body compressed, elevated in the middle ; scales small, rhombic, distinct on 

 inner surface of skin, obscured by minute spines roughening the outer surface ; sides of tail 

 with 4 or 6 hooked spines in 2 or 3 rows, smaller or absent in females. Lateral line absent or 

 indistinct. Teeth, six broad, flat, sharp-edged incisors in outer row of each jaw, and four, forming 

 an inner row, in upper jaw, alternating, one between the 1st and 2nd, and the other between the 

 2nd and 3rd on each side of the outer row. Fins : 1st dorsal composed of one large, thick, 

 rough, bony spine, which may be fixed in erect position or lowered into a pit on back, over the 

 eye ; membrane very small, triangular at base, with or without a second, small, rudimentary 

 spine : soft dorsal and anal long and low, with simple unbranched rays ; pectoral small, 

 rounded ; caudal rounded ; ventrals replaced by a small spine, sometimes rudimentary or 

 absent. Branchial slit in front of base of pectoral. No barbel to chin. Tropical and sub- 

 tropical seas.] 



D. 33 to 34 ; A. 33; P. 12; C. 12. 



Description. — Body sub-ovate, compressed; profile of forehead slightly con- 

 cave between eye and snout, rising- with gentle convexity to origin of second dorsal 

 at an angle of about 30°. Lower lip slightly protruding- beyond the upper. 

 Greatest depth of body about twice and a half in total length, including- caudal fin. 

 Eye large, a little below frontal edge; branchial slit oblique, slightly longer than 

 diameter of eye, lower end in front of upper base of pectoral. First dorsal spine 

 with its anterior base over middle of e} r e, thick, strong, quadrate in section, slightly 

 arched forwards, about half the length of from anterior edge of orbit to mouth; the 

 four edges set with about 15 conical spines arched downwards and outwards, those 

 on two anterior ridges nearly three times as large as those on posterior ridges, which 

 are more equal, numerous, and closer; a row of smaller spines on base of front and 

 lateral faces. One very small ray in membrane behind the great spine; pelvic spine 

 at end of long bony ridge of ventral edge very small, with a few rounded granules 

 on middle, and 4 or (J triangular spines on posterior end directed backwards; 

 abdominal edge from pelvic spine to anus convex or concave according to tem- 

 porary causes, ventral edge rising abruptly from end of spine to front of anal fin. 

 Fins: Pectoral semi-oval, of 12 rays; dorsal high, moderately convex, of 34 rays, 

 increasing in height to ninth ray, gradually decreasing thence to posterior end; 

 anal of 33 rays, moderately deep, rounded, rays lengthening gradually to sixth or 

 seventh, gradually diminishing to posterior end; caudal fin narrow, rounded, of 

 12 thick, branched, spinulose rays. Skin: With oval scales, marked with radiating, 

 close, branched ridges, each scale having from its centre a long, thick, cylindrical 

 spine obliquely dilated and subtruncated at an obtuse angle in front, leaving an acute 

 point directed backwards at the tip, in most portions of the body; but, in a few places, 

 terminating in an arched, acute, spinous tip with the dilatation lower down on the 

 stem. In specimen described no "tooth-brush" group of bristle-like spines on sides 



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