^ 



— 151 — 



of ankylosis with it. Ventrally it is in contact with the fourth infraorbital. Posteriorly its ventral 

 half abuts against the dorsal portion of the anterior edge of the preopereular, its dorsal portion abutting 

 against the anterior edge of the suprapreopercular bone. The dorsal end of the fifth infraorbital 

 does not quite reaeh the lateral end of the postfrontal. 



3. SUSPENSORIAL APPARATUS AND MANDIBLE. 



The PREOPERCULAR is a large, stout and irregulär bone. On its outer surface, slightlv 

 below its middle point, there is a thin and relatively tall ridge, already referred to, which crosses 

 the bone horizontally, from one edge to the other, increasing gradually in height from in front back- 

 ward; and that part of the bone that lies ventral to the ridge inclines ventro-mesially at a marked 

 angle to the part that lies dorsal to it. The bone is traversed by the preopereular latero-sensory 

 canal, that canal presenting two straight limbs, a dorsal and a ventral one, which unite at an 

 angle that lies beneath the horizontal ridge on the outer surface of the bone. The canal lodges six 

 sense organs. 



On the inner surface of the preopereular, following the angular course of the latero-sensory 

 canal, a f lange arises from the bone, the dorsal portion of this f lange projeeting antero-mesially and 

 the ventral portion projeeting dorsally or dorso-mesially, the two portions of the flange lying at 

 the same marked angle to eaeh other that the two limbs of the latero-sensory canal do. In the angle 

 between the two portions of the flange there is a coneave surface which lodges the cartilaginous inter- 

 space between the hyomandibular and symplectic. Dorsal to this coneave surface, in the angular 

 space between the dorsal limb of the flange and the internal surface of the anterior edge of the bone. 

 this angle being presented anteriorly, the ventral three-fifths of the hyomandibular is lodged. Against 

 the lateral, or dorso-lateral surface of the anterior half of the ventral limb of the flange, the broad 

 Hat ventral surface of the posterior process of the quadrate rests; both the quadrate and the hyoman- 

 dibular being firmly attached to the preopereular. 



The HYOMANDIBULAR has, in alcoholic speeimens, two dermal bones almost inseparablv 

 fused with its outer surface. The lines of Separation between these dermal bones and the underlving 

 hyomandibular can be everywhere traced, but the two bones cöuld not be removed, without breakage, 

 in any of the speeimens examined, all of which had been preserved in alcohol and then slightlv boiled. 

 One of these two dermal bones is the fifth one of the infraorbital series, and the other the supra- 

 preopercular. As already stated, the bind edge of the fifth infraorbital bone rests upon the lateral 

 surface of a flange on the anterior edge of the hyomandibular. This flange arises from a stout longi- 

 tudinal ridge on the lateral surface of the bone — this ridge being the homologue of the one already 

 described in the other fishes of the group — and between the flange and the anterior edge of the 

 body of the bone there is a V-shaped space, the hollow of the V directed anteriorlv and forming the 

 bind end of the flat space included, as in Trigla, between the cheek-bones, externallv, and the palato- 

 quadrate internally. In the hollow of this V, near its ventral end, and hence anterior to the longi- 

 tudinal ridge on the lateral surface of the bone, the canal for the hyoideo-mandibularis facialis opens, 

 having traversed the bone from its internal surface. The longitudinal ridge on the lateral surface 

 of the bone inclines backward, its summit fitting into the V-shaped groove on the anterior edge of 

 the dorsal limb of the preopereular. The fifth infraorbital was broken and pieked off in the speeimen 

 used for the figures. 



