EEPORT OX THE DEEP-SEA FISHES. 191 



Tlie question of tlie homology of the luminous organ and its covering lamellae is still 

 obscure ; and no other specimen can be sacrificed to investigate the osteology of the 

 skull. If, as Professor Moseley's investigations seem to prove, the luminous organ is not 

 a modification of the eye, as Mr Murray and myself supposed at first, and if the organ of 

 vision with the optic nerve has disappeared, the luminous organ is probably the 

 homologue of that which is found in some Scopelids between the eye and nostril, and the 

 covering plates would be the homologues of the prseorbital membrane bones. With the 

 abortion of the eyes the luminous organs with their praeorbitals would have moved from 

 their usual lateral position to the top of the head. 



Ipnops murrayi (PI. XLIX. fig. B). 



, Ipnops murrayi, Giintli., Ann. and Mag. Nat. Hist., 1878, vol. ii. p. 187. 



B. 12. D. 10. A. 13. P. 14. V. 8. L. lat. .55. 



Body elongate, cylindrical, tail compressed behind, head depressed. The depth of 

 the trunk diminishes but little backwards, and is contained thirteen and a half times 

 in the total length, without caudal; the length of the head is one-sixth of the total. 

 Head broad, much broader than deep, its greatest depth being two-thirds of its length. 

 Snout broad, much depressed, with obtusely rounded anterior profile ; cleft of the mouth 

 very wide, the maxillary moderately dilated behind and extending beyond the middle 

 of the length of the head. Mandible projecting beyond the upper jaw, broad, but owing 

 to the depressed form of the snout its outer surface is nearly entirely at the lower side 

 of the snout. Infraorbital chain of bones very narrow, wedged in between the trans- 

 parent lamina and the maxillary, with four very distinct apertures leading into the 

 mucous duct. The upper surface of the head, including the snout, is wholly covered by 

 the two cornea-like laminae of the luminous apparatus. They are closely attached to 

 each other along the median line, each being divided by a shallow transverse ridge into 

 a larger anterior and a smaller posterior portion. The ridge turns forward near and 

 parallel to, the median line, and marks the course of a superficial mucous duct. 



The gill-laminae are well developed and the gill-rakers long, needle-shaped, closely 

 set, about twenty-two in number on the outer branchial arch. 



The vent is nearly twice as distant from the root of the caudal fin as from the end 

 of the snout, and rather more than the length of the head from the gill-opening ; it is 

 placed between the ventral fins. 



The dorsal fin commences immediately behind the vertical from the vent ; it is short, 

 but its longest rays are twice as high as the body. Origin of the anal midway between 

 the vent and the root of the caudal, composed of rays which are still more slender and 

 shorter than those of the dorsal. Caudal fin narrow, subtruncated, more than half as long 

 as the head. Pectorals rather feeble, lateral, as long as the caudal, and extending to the 



