STERNOPTYCHID^E. 47 



35° 17' south, longitude 17° 43' east, two Scopeli were caught; one had some life 

 remaining and displayed a faint, though an undoubted luminosity in the pearly 

 bodies of the pectoral region : direct irritation had no effect. Professor Leuckart, 

 in 1865, suggested whether some at least might not be regarded as accessory organs 

 of sight, a position shown by Leydig to be untenable. In 1879 Dr. Ussow (Bnll. 

 Soc. Moscow, liv, 1879, p. 79) of St. Petersburgh, remarked that among these fish 

 belonging to seven genera which he had examined these organs could be arranged 

 in two series : the first he regarded as constituting accessory eyes, the second as 

 special glandular organs. Leydig, in 1881 (Die augen. Organe der Fische, Bonn.), 

 added another group, viz., mother-of-pearl like organs, which are not sensory in 

 function, and he considers they bear the closest resemblance to the electric, or 

 pseudo-electric organs of other fishes, with probably a secondary illuminating 

 function. 



Group A. — PseudobranchisD present. A rudimentary spinous dorsal fin. Body 



scaleless. 



Genus I — Argyropelecus,* Cocco. 



Pleurothysis, Lowe. 



Branchiostegals nine : pseudobranchim present. Head large, it and the trunk 

 elevated and very compressed, the latter passing suddenly into the tail which is 

 narrow. Eyes large, directed upwards and outwards, separated by a very narrow 

 interspace. Cleft of mouth vertical and deep, with the lower jaw prominent. The 

 margin of the upper jaw is formed of the premaxillary and maxillary, which have a 

 single row of fine teeth, a row also in the lower jaw. First dorsal short, preceded by 

 an osseoths plate formed from neural spines : adipose dorsal, if present, rudimentary. 

 Pectorals well developed. Ventrals small. Gill-openings wide : gill-rakers long. 

 Body covered with a silvery pigment but no distinct scales. Humeral arch and pubic 

 bones prolonged into flat, pointed processes, which project along the median line of 

 the abdomen, intei'mediate between which are some scutes. Air-bladder present. 

 Four pyloric appendages. 



Examples of this genus are said to have been dredged in the Challenger 

 expedition at 1100 fathoms, a statement upon which discredit has been thrown. 

 In the Mediterranean it would appear not to be found at very great depths, and 

 may be a night feeder, at which time it ascends to the surface as is seen in the 

 Scopelido3. 



Geographical distribution. — Atlantic Ocean and Mediterranean. One species 

 has been found off the coast of Norway. 



1. Argyropelecus hemigymnus, Plate CIX, fig. 1. 



Argyropelccus hemigymmts, Cocco, Giorn. Sc. Sic. 1829, fasc. lxxvii, p. 146 ; 

 Bonap. Faun. Ital. Pesc. ; Cuv. and Val. xxii, p. 398 ; Giinther, Catal. v, p. 385, 

 and Ann. and Mag. (4) 1874, xiii, p. 139; Canestr. Fauna Ital. p. 119; Moreau, 

 Poiss. France, iii, p. 498 ; Giglioli, Pesc. Ital. p. 39. 



Sternoptyx Mediterranea, Cocco, Giorn. il Faro, 1838, iv, p. 7, f . 2 ; Bonap. 

 1. c. c. fig. 



Sternoptyx hemigymnus, Cuv. Reg. Anim. 111. Poiss. pi. ciii, f. 3. 



B. ix, D. 6 -f- 7-8, P. 10, V. 6, A, 11-12, C. 19. 



The greatest height of the body equals half the total length. Posterior to the 

 vent the caudal portion of the body becomes abruptly narrowed, while it is 

 everywhere compressed, its greatest width merely equalling 1/4 of its height. 

 Caudal fin 1/5 of the total length. Eye — high up, directed outwards and slightly 



* From some error, Agassi/, thought this might he the young of Zeus fdber. 



