the hyomandibular articulates by fibrous tissue with the 

 anterodorsal head of the operculum. Anteriorly the 

 hyomandibular ends in the cartilaginous plate between it 

 and the metapterygoid. 



Quadrate. — Wide posteriorly, tapering anteriorly 

 to a head for articulation through fibrous tissue with the 

 articular of the lower jaw; cartilage filled along posterior 

 edge; with a long posteriorly directed process from its 

 posteroventral region which articulates by inter- 

 digitation and fibrous tissue with the anteroventral edge 

 of the symplectic in large specimens, whereas in smaller 

 specimens intimate contact between the symplectic and 

 posterior extension of the quadrate is not made and the 

 articulation is purely by fibrous tissue. Along the pos- 

 terior edge the quadrate articulates through cartilage 

 with the anterior edge of the metapterygoid, at this 

 region being cartilage filled. Ventrally the quadrate ar- 

 ticulates through fibrous tissue with the dorsal surface of 

 the anterior end of the preoperculum. 



Metapterygoid. — A more or less flat plate; cartilage 

 filled along its anterior, ventral, and posterior edges; ar- 

 ticulates through cartilage anteriorly with the quadrate, 

 while along its ventral edge it extensively interdigitates 

 with the symplectic in large specimens but only ar- 

 ticulates to it through fibrous tissue in smaller 

 specimens. Posteriorly the metapterygoid articulates 

 through cartilage with the hyomandibular. 



Symplectic. — Long and rod-shaped; cartilage filled 

 at its posterior end; articulates dorsally by inter- 

 digitation (in large specimens, see above) with the 

 metapterygoid and anteriorly variously through inter- 

 digitation and fibrous tissue with the posteroventral end 

 of the quadrate. Posteriorly the symplectic is in contact 

 with the cartilaginous plate between the metapterygoid 

 and hyomandibular. The upper end of the epihyal is at- 

 tached by fibrous tissue to this cartilaginous plate im- 

 mediately behind the posterior end of the symplectic. 

 Ventrally the symplectic articulates by fibrous tissue 

 with the dorsal surface of the preoperculum. 



Palato-Pterygoid Region. 



Palatine. — Cartilage filled at its extreme posterior 

 end; articulates by fibrous tissue anteriorly with the dor- 

 solateral surface of the maxillary, medially with the 

 lateral surface of the expanded portion of the vomer, 

 posteroventrally by fibrous tissue to the posterior end of 

 the ectopterygoid, and directly posteriorly through car- 

 tilage and fibrous tissue to the anterodorsal region of the 

 metapterygoid. The posterodorsal wing of the palatine 

 connects to a broad band of fibrous tissue that runs over 

 and above the premaxillary pedicels to join with the 

 posterodorsal wing of the palatine on the other side. Al- 

 though not sutured to any of the surrounding bones the 

 palatine is in effect firmly held in place by its extensive 

 fibrous tissue articulations. 



Ectopterygoid. — Somewhat in the shape of an 

 elongate rectangle; articulates along all of its ventral 

 edges by interdigitation with the quadrate. Dorsally it 

 articulates by fibrous tissue with the posteroventral 

 region of the palatine and posteriorly through cartilage to 

 the anterodorsal region of the metapterygoid. 



Mesopterygoid. — Absent in this and all other species 

 of triacanthids with the exception of Trixiphichthys 

 weberi, in which it is a small plate of bone closely inter- 

 digitated to the posterior third of the dorsal edge of the 

 far larger metapterygoid. 



Opercular Region. 



Operculum. — A thin sheet of bone broadest in the 

 middle and tapering to a point ventrally; with a short 

 dorsally prolonged flange above its anterodorsal head 

 which articulates by fibrous tissue with a groove on the 

 posterior edge of the hyomandibular just above the dor- 

 sal tip of the preoperculum. Ventrally the operculum 

 slightly overlies and articulates by fibrous tissue with the 

 suboperculum. 



Suboperculum. — Rounded anteriorly, tapering to a 

 dorsally directed point posteriorly; articulates by fibrous 

 tissue dorsally with the operculum and anteriorly with 

 the interoperculum. 



Interoperculum. — Very elongate and flat; rounded 

 posteriorly but tapering to a point anteriorly; articulates 

 by fibrous tissue posteriorly with the suboperculum and 

 anteriorly ligamentously with the angular in the lower 

 jaw. In the posterior half of its length the dorsal edge of 

 the interoperculum connects by a band of fibrous tissue 

 to the epihyal in the region where the epihyal articulates 

 with the interhyal. 



Preoperculum. — Slightly expanded posteroven- 

 trally in the region below the hyomandibular; the dorsal 

 edge along the anterior half of the bone slightly thicken- 

 ed for articulation by fibrous tissue with the quadrate; 

 articulates dorsally in about the middle of its length 

 variously by fibrous tissue and through cartilage with the 

 symplectic, metapterygoid, and anterior end of the 

 hyomandibular, whereas the main articulation to the 

 hyomandibular is by fibrous tissue along the posterodor- 

 sal edge of the preoperculum. 



Upper Jaw. 



Premaxillary. — L-shaped, with the long dorsal arm 

 (pedicel) much longer than the ventral arm and movably 

 articulated by fibrous tissue along the dorsal surfaces of 

 the vomer and the extreme anterior end of the ethmoid, 

 allowing for a slight protraction of the upper jaw. When 

 fully retracted, the pedicel reaches to the anterior basal 

 region of the ethmoid. The shorter ventral arm of the pre- 

 maxillary forms the upper two-thirds of the anterior edge 

 of the upper jaw, the rest of the border being formed by 



