ALEPISAUROID AND MYCTOPHOID FISHES 323 



by all alepisauroids, namely, the premaxillae each carry a single row of teeth and there are one or two 

 rows of teeth on each palatine and 1-3 rows on each dentary. 



Turning now to more recent studies, Harry (1953 a) stated that the symphysis of the lower jaw is 

 more or less elevated in the Paralepididae, fitting into a corresponding, arched toothless emargination 

 on the upper jaw. As Harry has pointed out elsewhere, the symphysis of the upper jaw is usually 

 toothless in the Alepisauroidea and may be arched. (A specimen of Evermannella balbo which I ex- 

 amined had an arched symphysis provided with teeth.) It is also of interest that certain of the Mycto- 

 phoidea have a bony boss at the symphysis of the lower jaw, which fits into a toothless emargination 

 of the upper jaw (Chlorophthalmidae, Bathypteroidae, Ipnops, Bathymicrops, Notosudis, Luriosudis 

 and Neoscopehis). In many of the Myctophidae there is certainly a small bony boss at the symphysis 

 of the lower jaw, but this fits against a toothless, slightly depressed area between the two premaxillae, 

 but such close-fitting structures are absent in the jaws of the Aulopidae, Harpadontidae and Syno- 

 dontidae. 



Harry (1953 a) has also drawn attention to the form of the gill-rakers in the Alepisauroidea. In 

 Magnisudis each gill-raker consists of a basal part bearing four long, stiff, depressible, filamentous parts. 

 The rakers of Alepisaurus ferox are somewhat similar, each consisting of a basal part supporting a 

 number of spines, of which one to four are longer than the others. Needle-like or spinous gill-rakers 

 are also found in Paralepis, Oinosudis and Evermannella. 1 In Scopelarelius, Notolepis, Lestidinm, 

 Macroparalepis and Sudis the rakers are tooth-like. All the gill-arches in Anotopterus are without 

 rakers. 



More normal lath-like gill-rakers are characteristic of all families of the Myctophoidea, except the 

 Harpadontidae and Synodontidae, these having tooth-like or spinous rakers. 



There is therefore much justification for the opening remarks concerning the difficulty of defining 

 the suborders Myctophoidea and Alepisauroidea, but before summarizing this discussion in a 

 section on alepisauroid relationships, there are certain interesting morphological trends within 

 this group which will now be considered. Points of contrast with the myctophoids will then be seen. 



The swim-bladder. A survey of the literature and a number of dissections {Alepisaurus ferox, 

 Anotopterus pharao, Omosudis lowei, Evermannella atrata, Scopelarelius guentheri and Notolepis coatsi) 

 show that a swim-bladder is absent in the Alepisauroidea. In the Myctophoidea this organ is only 

 found in the Myctophidae, Marshall (1951 and unpublished) finding a closed swimbladder in twenty- 

 three of the twenty-six species studied. The absence of the swim-bladder in the Aulopidae, Chloro- 

 phthalmidae, Synodontidae, Harpadontidae, Ipnopidae and Bathypteroidae was recorded by Gunther 

 (1864, 1887). 



Correlations between environment and the degree of development of the swim-bladder (including 

 its loss) in teleosts have already been considered by Marshall (1950, 1951) and Jones and Marshall 

 (1953), but in these papers little reference was made to the alepisauroids. 



The Alepisauroidea are active, voracious, mid-water fishes, while the Myctophoidea, other than the 

 Myctophidae and Notosudidae seem to be predominantly bottom-dwellers. Many benthic fishes lack 

 a swim-bladder, but the absence of this organ in a mid-water group, such as the Alepisauroidea, is of 

 interest and will be further considered. Marshall (1951 and unpublished) has found a well-developed 

 swim-bladder in many of the bathypelagic fishes, which have centres of abundance in the uppermost 

 1000 m. of the ocean. But notable exceptions to this rule are found in the Melanostomiatidae, as well 

 as in the Alepisauroidea. (A consideration of the reports by Ege, 1930, Legendre, 1934, and Maul, 

 1945, supports the view that many paralepidids occur in the uppermost 500 m. and the same would 



1 In the specimen of Evermannella balbo examined, there are no rakers on the first gill arch but some are present on the 

 second arch. 



55. 



