242 THE VOYAGE OF H.M.S. CHALLENGER. 



portion of the head and equal to the width of the interorbital space. Maxillary not 

 reaching to the front margin of the eye. The length of the head equals its distance 

 from the root of the ventral, the origin of which is but slightly in advance of that of 

 the dorsal. Nearly all the scales are lost, only some of the lateral line remain. They 

 are much larger than the other scales ; and on the tail, where the lateral line approaches 

 the lower profile, these larger scales are separated from the anal fin by one series of 

 small scales only. Otherwise, there is the greatest similarity between this species and 

 Halosaurus rostratus. 



Distance of the snout from the mouth, . . ■ ... 5| lines. 



Distance of the snout from the eye, 



Distance of the snout from the root of the pectoral fin, 



Distance of the snout from the root of the ventral, . ■ 



Distance of the snout from the origin of the dorsal, . 



Distance of the snout from the vent, . ' 



Total length, ..... 



Habitat.- — South of Japan, Station 235 ; depth, 565 fathoms. Two specimens, 

 16^ inches long. 



This species is so closely allied to the preceding that it would appear to be 

 sufficient to refer to the following points only : the band of palatine teeth is not broader 

 than tiaat of the intermaxillary, only slightly separated from that of the other side, and 

 somewhat distant from the pterygoid teeth. The scales of the lateral line are about 

 three times the size of the others, and twenty -nine in number between the gill-opening 

 and the vent. They seem to have been provided with a luminous organ, but it must 

 have been very thin and much less developed than in the other species, as only traces 

 of it remain on the few scales which have been preserved. 



The body of the fish is light-coloured ; the head, vent, and hind part of the tail 

 black. 



Family Notacanthi. 



In placing the Notacanths in the present work between the Halosauridas and 

 Mursenidse I do not intend to convey the impression that I consider them to be specially 

 allied to either of these Physostomous families. There is no other type of Acantho- 

 pterygians by which they would be connected with that order, whilst the truly abdominal 

 position of their many -rayed ventral fins offers sufficient grounds for removing them to 

 the Physostomi. On the other hand, there does not seem to be an oj)en communication 

 between the air-bladder and the oesophagus, at least in Notacanthus sexspinis. As I 



