DEALFISH. 



!17 



wards, thin, sniaJl, -witli few rays and rounded at the 

 ti]i, tlie first ray hemg extremely sliort, the second the 



thickest and the fifth the longest". T 



head 



IS com- 



paratively small, its length beii:g always less than flie 

 greatest depth of the body''; hut flie eves are large", flat- 

 tened to the plane of the cheeks, and set about half-way 

 up the body, the distance between them and the frontal 

 l>rofile being equal to their radius. The pupil is oblong 

 and set obliquely downwards in a backward direction. 

 When the mouth is closed, the head, when seen 

 from tlie side, is of a (juadrilateral shape. The straight 

 profile of the forehead and snout slopes downwards al- 

 most at a right angle to the ascending under surface 

 of the lower jaw, the ])oint of whieli projects, however, 

 beyond the upper ja\\-. The cornei-s of the mouth are 

 now entirely hidden at the sides, being covered by the 

 intermaxillary and the maxillary bones; but the upper 

 margins of the lower jaw rise vertically within the gape. 

 The hind corner of the head, formed by the suboper- 

 culum, is somewhat rounded and elongated. The lower 

 corner of the square is formed by the angular part of 

 the lower jaw, which is produced behind into a blunt 

 spine''. The cheek is naked; only in front of the eye 

 do we find two suborbital or preorbital bones, the lower 

 being so narrow that it only just separates the eye 

 from the point of the high, triangular branch of the 

 lower jaw, which, in its turn, is covered by the broad, 

 thin maxillary bone^ The latter, like all the opercular 

 bones, is of a thin, spongeous textui'e, externally ca- 

 vernous, with radiating elevated ridges. It is obliquely 

 linguiform, the breadth beinir rather more than half 

 the length. The preoperculum is crescent-shaped, the 

 operculum almost like the upper half of the pi-eoper- 

 culum in shape, the part of the suboperculum Avhich 



is externidh' visible, narrow, and tiie interoperculum, 

 which i'oi'ins the greater jtart of the lower margin of 

 the gill-cover, of fairly uniform breadth. All these 

 bones are nieniljranous at the margin. The gill-open- 

 ings ai'e large, tiieii- height' being about e(|ual to the 

 total length of the interoperculum and suboperculum. 

 The Ijranchiostegal membrane is united to the narrow 

 isthmus back to a point vertically below the hind mar- 

 gin of the eye; but in front of this point it hangs in 

 a fold across the isthmus, thus appearing double, when 

 the jaws are drawn back. At these times too, it is co- 

 vered, together with the whole of the branchial appa- 

 ratus and the isthmus, Ijv the interopercula and the 

 branches of the loAver jaw. 



But the appearance of the head is quite different 

 when the mouth is protruded. The nasal processes^ of 

 the intermaxillary bones extend right up to the occi- 

 put, where they mav slide to and fro in the deep groove 

 in the frontal l)oiies. When they are pi'otruded, they 

 draw Avith them the maxillarA' Ijones, which are oidv 

 loosely connected with the palate, and are thus capable 

 of extensive protrusion. The snout now attains a length 

 which may even exceed that of the rest of the head, 

 and acquii-es an appearance, Avhen seen from the side, 

 not unlike that of a swine's snout. Now, when the 

 branchial apparatus is expanded, the hj'oid bone, to- 

 gether with the broad ceratohyoid bones, projects down 

 below the isthmus, and the branchiostegal membrane 

 emerges from the opercular apparatus. 



The nostrils are comparatively small, the posterior 

 being long, Init narrow, and situated in the form of a 

 perpendicular slit close to the anterior upper margin 

 of the orbit. The anterior nostril is separated from it 

 by a dermal l)ridge. 



Their lenfrth is nearly 4 % of that 



"' Tlie pectoral fins are perfect in a specimen caught in 1879, on the Ite of Vinga (Gothenburg), 

 of the body or '/j of the greatest depth of the latter. 



* In the specimen from Vinga (025 mm. long) the length of the head, measured from the middle of the margin of the upper jaw 

 (the tip of the snout), when drawn back, is ITS % of that of the body. This coincides with Lvtken's measurement of a Trachypterits 

 ardicus 830 mm. long, and also with Emery's measurements of the largest specimens of Track, iris in his possession (1,120 — 1,410 mm. 

 long). According to LCtken, however, in specimens of Trach. arcticiis about 1 m. in length, the average length of the head is 14'2 % 

 thereof, in specimens about 13 dm. long, 12"4 %, and in specimens about 2 m. long, 111 °o. 



'' In specimens about 1 m. long the longitudinal diameter of the orbit is about 30 \ of the length of the head. In specimens I'/o 

 m. in length it may sink to 25'8 % of the length of the head, according to LOtkes. In many cases, however, the eye on the one side of 

 tlie head is at least somewhat larger than that on the other. 



'' In the specimen from Vinga the length of the right branch of the lower jaw is 57 'i of that of the head, of the left only 52Y2 /»• 

 Though the snout has been damaged, this does not seem enough entirely to explain the difference. In the other two specimens preserved in 

 spirits in the Royal Museum, however, there is no such difference: but the gape is crooked when the mouth is protruded. 



■■ In the specimen from Vinga the length of the right maxillary bone is 40 % of that of the head, of the left only 34-3 %. Cf. 

 the preceding note. 



•'' In the specimen from Vinga the height of the gill-openings is - 3 of the length of the head. 



'■' In the specimen from Vinga the length of the nasal processes, together with the anterior height of the body of the intermaxillary 

 bones, is 75 mm. or very nearly * ., of the length of the head. 



