46 PHTSOSTOMI. 



Ordee in— PHYSOSTOMI, Miiller. 



All the fin rays articulated, with the exception of the first in the dorsal and 

 pectoral, which are frequently more or less ossified (some genera belonging to the 

 family Sternoptychidse have a rudimentary first dorsal fin). Ventral fin when 

 present abdominal and spineless. Air-bladder when existing having a pneumatic 

 duct (except in the family ScombresocidSB). 



Family, I— STERNOPTYCHIDiE. 



Margin of the upper jaw formed partly by the premaxillaries and partly by 

 the maxillaries, both of which are provided with teeth. Opercular bones not 

 fully developed. Gill opening wide: pseudobranchise present or absent. An 

 adipose dorsal fin may be present or rudimentary. Body scaleless or scaled. 

 Rows of round luminous bodies along the lower surface of the abdomen, and 

 occasionally some also on various parts of the body and head. Air-bladder when 

 present, simple. Eggs enclosed in the sac of the ovaries, and excluded by 

 oviducts. 



These fishes are all of small size and appear to be mostly pelagic, while some 

 may be abyssal forms. 



This family has been subdivided into three groups by Dr. Giinther, who, 

 however, failed to detect scales in Maurolious, in which genus they are present, 

 but deciduous. The divisions would consequently have to be altered as follows : 



Group A.— Pseudobranchise present: a rudimentary spinous dorsal fin 

 Scaleless. Stemoptychina. 



1. Argyropelecus. — A single row of teeth in the jaws. 



Group B. — Pseudobranchise present : no spinous dorsal fin. Scaled. Cocda. 

 2. Maurolious. — Lower jaw prominent. 



Group C— PseudobranchisB absent : no spinous dorsal fin. Scaled. ChauUodontina. 



The two forms of this family, Argyropelecus and Maurolicus, which have been 

 obtained off the coasts of Great Britain and Ireland, in common with some other 

 pelagic forms found elsewhere, possess eye-like spots of a circular form which 

 are either impressions or prominences on the skin. Their uses have been a 

 fertile subject for speculation, and possibly much still remains to be discovered. 

 MacGulloch remarked that considering at a depth of 800 or 1000 feet, the 

 light of the sun ceases to be transmitted in the ocean, it may be that animal 

 luminousness is a substitute for that light, and if so these organs would take the 

 place of minature lanterns. Professor Reinhardt observed of Astroneth.es Fieldii, 

 Val., which is common in the Atlantic Ocean between 23° and 6° north latitude, 

 that in two instances he captured the fish alive, when he saw that it sent forth two 

 strong and vivid greenish lights, which intermitted momentarily and ceased 

 altogether when the fish died (Zool. 1854, p. 4300). Dr. Guppy (Ann. and Mas;. 

 Nat. Hist. March, 1882, p. 202) remarked that on November 7th, 1881, latitude 



