68-4 FISHES. 



FiEST Family — Sclerodermi. 



Snout someivhat j^'i'oduced ; jmvs armed with distinct teeth 

 in small nuniber. Skin with scutes or rough. The elements of 

 a spinous dorsal and ventral fins generally 'present. 



Marine fishes of moderate or small size, very common in 

 the tropical zone, but scarcer in higher latitudes. They have 

 been found in three localities of tertiary strata, viz., at Monte 

 Bolca, where a species of Ostracion occurs, and in the Schists 

 of Glaris, from which two genera have been described, Acan- 

 thoderma and Acanthopleurus, closely allied to Balistes and 

 Triacanthus. Glyptoccphalus from the Isle of Sheppey has 

 the skull of a Balistes, but its body is covered with tuber- 

 cles arranged in regular series. The Scleroderms may be 

 divided into three very natural groups : — 



A. Triacanthina. — The skin is covered with small, rough, 

 scalelike scutes. A spinous dorsal fin with from four to six 

 spines. A pair of strong, movable ventral spines, joined to the 

 pelvic bone. 



To this group belong the genera Triacanthodes, Hollardia, 

 and Triacanthus, represented by five species, of which Tria- 

 canthus hrevirostris from the Indian Ocean is the most 

 common. 



B. Balistina. — Body compressed, covered with movable 

 scutes or rough. Spinous dorsal reduced to one, two, or three 

 spines. Ventral fins reduced to a single pelvic prominence, or 

 entirely absent. 



To this group belong the genera Balistes, Monacanthus, 

 and Anacanthus, tlie last genus being distinguished by a bar- 

 bel at the lower jaw. 



Balistes, or the " File-fishes " proper, inhabit the tropical 

 and sub-tropical seas ; shoals of young are not rarely met with 

 in mid-ocean. Some thirty species are known, many attaining 

 a length exceeding two feet; but the majority are much 



