696 



SfANIJlN AVIAN FISHES. 



is angular, and forms with tlie sliortei' (inner) arm a 

 ])art of the outer margin of the orijit. These two sub- 

 orbital bones thus foi'iii with tlieii' outer parts an osseous 

 ridge projecting from tlie orbital ring, a structure i"e- 

 minding us of that which in the Cottoids and the Lump 

 Suckers unites the orbital ring to the preoperculum. 

 The foui'tli suborbital bone, which is the longest, is 

 curved in an S-shape. \\\t\\ its lower curve it forms 

 a part of the lower (outer) and the whole of the pos- 

 terior margin of tiie orbit. \Y\i]\ its U])per curve it 

 bends backwards to be united by ligaments to the out- 

 side of tlie anterior extremity of the posterior frontal 

 bone, which at this point, outside the frontal bone pro- 

 per, meets the hind extremity of the lateral ethmoid 

 (prefrontal) bone. 



The crescent-shaped, obliquely set preopercula are 

 also externally indistinct, being entirely covered by the 

 skin; but a distinct dermal fold on each side marks the 

 position of the margins of the opei'culum and interoper- 

 culum. Tiie former is triangular, witli tiie up|ier margin 

 convex and the lower posterior margin slightly concave. 

 The interoperculum too, which also replaces the suboper- 

 c'ulum, is triangular in form, but forked behind, •\\itii 

 the upper posterior corner projecting obliquely under the 

 openruluin. Tiie anterior extremity of the interoper- 

 culum is united by a long and strong ligament to the 

 hind extremity (angular part) of the lower jaw; but this 

 ligament runs along the inside of the interoperculum as 

 well, and is attached here and also, no less firmly, to 

 the outside of the upper part of the cpihyoid bone". 

 Behind the said dermal fold marking the hind mar- 

 gin of the opercular apparatus proper, the head is con- 

 tinued on each side by a broad branchiostegal membrane, 

 which lies in a rather indistinct flap above the upper 

 angle of the base of the ]jectoral hn. Both of the 

 branchiostegal membranes are entirely free from the 

 isthmus and united to each other only at the extreme 

 front for a \ery short distance, nearly below the corners 

 of the mouth; but the left branchiostegal membrane 

 overlaps the right under the isthmus to a considerable 

 extent. Tiie branchiostegal rays are luimerous; 13 or 

 14 of them are set on the ceratohyoid bone and are 



fairly unifoi-m in thickness and terete, but nari'ow and 

 pointed. The last two of these rays are set on the cpi- 

 hyoid bone, and the last in particular is flat towards 

 the tip, externall)' grooved (hollowed in a longitudinal 

 direction), and fairly broad. 



The cards of teeth in tlie lo\ver jaw, on the inter- 

 maxillary bones, and on the head of the vomer are of 

 similar form and jjarallel, curved like a crescent and of 

 fairlv unifoi-m breadth, but growing narrower as usual 

 beliind (distally on the vomer). They are composed of 

 dense, pointed, and somewhat recurved tcetii of uniform 

 size, which are coni|>arativeh' small, l)ut in so large a 

 fish still form a po\\erful weapon. In the lower jaw 

 and on the intermaxillary bones the halves of the cards 

 are separate in front; but the vomerine card of teeth 

 presents an unbroken surface''. Of the three upper pha- 

 ryngeals on each side only the hindmost is furnished 

 with teeth, and this bone is also the only one of the 

 three that is visible in the jiharynx, having extended 

 under the other two, which are small and serve to sup- 

 jjort it and to attach it to the under surface of the skull. 

 The patch of teeth on the first-mentioned pharyngeal is 

 fairly large, convex and elliptical. I'acli of the two 

 lower ](hai'yngcals is furnished witli an oblong patch of 

 tectii, broader in front, narrower l)eliiiKl (above), and 

 concave on the inside''. All the pharyngeal teeth are 

 pointed and resemble the jaw-teeth, but are smaller, 

 smallest on the lower pharyngeals and in the outer pos- 

 terior corner of the upper cards. The gill-rakers are 

 scattered and fairly short, but pointed like teeth. On 

 the first and second branchial arches they are set in a 

 single row, and on the front of the first arch ^^'e find 

 9 or 10 on the ceratobranchial bone and 2 on the lower 

 part of the epibranchial bone. In some cases the lower 

 pharyngeals are also furnished on their outer margin 

 with a I'ow of short, similar s]iines. The ])alatal folds 

 within the cards of jaw-teetli are well-de\elopcd, but 

 the upper is (piite shallow. The upper jaw is not ca- 

 pable of the slightest protrusion, for the intermaxillary 

 bones are firmly united by ligaments not only to the 

 large anterior process of the ethmoid bone proper, but 

 also, though at a somewhat greater distance, to the 



" Cf. above, p. 1)64, note i, on the singular position of tlie interoperculum in the Synyiuiihinw. 



'' In a Slientfish 2 metres long the patcli of teeth on each half of the lower jaw is 29 mm. broad in front and lis mm. long, though 

 the posterior (outer) part for a distance of 40 mm. is considerably narrower than the anterior part; the patch on each intermaxillary bone is 

 K5 mm. long and 22 mm. broad, a breadth also attained by the vomerine cord of teeth, which measured across the palate is 90 mm. in length. 



' In a Sheatfish 2 metres long each of the cards of teeth on the upper pharyngeals is 47 mm. long and 30 mm. broad, on the lower 

 jiharyngeals 8;') mm. long and 24 mm. liroad at the broadest |ioint. In a Sheatfish 1 metre long each of the two cards of teeth on the upper 

 pharyngeals is 30 mm. long and 21 mm. broad, on the lower pharyngeals 47 mm. long and 14 mm. broad at tlie broadest point. 



