322 DISCOVERY REPORTS 



concluded that in Antarctic waters Anotopterus lives, at least for part of the time, in the upper ioo m. 

 But little is known of the vertical limits of distribution and the possibility of tropical submergence 

 needs to be borne in mind. 



PART II. COMPARISON OF ALEPISAUROID AND 

 MYCTOPHOID FISHES 

 Although the Iniomi have been divided into the suborders Myctophoidea and Alepisauroidea, it is by 

 no means easy to assign clear-cut diagnostic features to these groups. Regan's (191 1) definition of the 

 Alepisauroidea was mainly based on the osteology of Alepisauras and Evermannella, and he placed the 

 paralepidid fishes and Sudis among the Myctophoidea and considered that Ateleopus should be put 

 into a third and separate suborder. 



Regan's use of the forward attachments of the palatines as a character for separating the alepisau- 

 roids and myctophoids cannot be sustained, as a study of Parr's (1929) paper soon shows. The degree 

 of development of the interoperculum (the smallness of this bone in the alepisauroids contrasting 

 with its more normal development in the myctophoids), is a trenchant distinguishing feature, as long 

 as Regan's inclusions within the Alepisauroidea of Scopelarchus, Evermannella, Omosudis, Alepisaurits 

 are accepted. But Harry (1951, 1953) has cogently argued that the Paralepididae show a closer rela- 

 tionship to the alepisauroids than to the myctophoids ; and in this family the interoperculum is well 

 developed (Parr, 1929). Furthermore, Anotopterus, which has many features in common with 

 Alepisaurus, differs from the latter in possessing a relatively large interoperculum. Similarly, the 

 preoperculum, which is narrow and almost vertically placed in the Scopelarchidae, Evermannellidae, 

 Omusodidae and Alepisauridae, is broad and boomerang-shaped in the Paralepididae and fairly wide 

 in the Anotopteridae. In both these latter families the preoperculum is obliquely inclined, following 

 the line of the forwardly directed suspensorium. 



Regan also based his classification on the design of the pectoral girdle, remarking that in the Mycto- 

 phoidea the cleithrum is attached to the lower end of the supracleithrum, while in the Alepisauroidea 

 the attachment comes at the upper end of the latter bone. As far as I have been able to extend this 

 observation, it seems true for the myctophoids in which a more 'solid' pectoral girdle is developed, 

 there being a firm join between the supracleithrum and cleithrum. In the myctophoids (Neoscopelus 

 and Lampanyctus crocodilus were examined) there is a wide area of overlap between these two bones, 

 the cleithrum extending rather beyond the midpoint of the supracleithrum. In the alepisauroids, 

 Omosudis, Evermannella and Alepisaurits the cleithrum is attached to the upper part of the supraclei- 

 thrum (Regan, 191 1 ; Parr, 1929), but in the paralepidids, although the above attachment is found in 

 Paralepis speciosa, Parr (1929) remarks that in Lestidium intermedium on the other hand the cleithrum 

 only extends somewhat above the middle of the supracleithrum. Again, in the figure of the pectoral 

 girdle of Scopelarchus anale (Parr, 1929), the cleithrum is shown to be attached to the lower end of the 

 supracleithrum. Clearly the type of linkage between these two bones cannot be used as a subordinal 

 diagnostic. 



The position of the pectoral fins was also listed as a distinguishing character by Regan, who pointed 

 out that these fins were laterallyplaced in the myctophoids but were low in position in the alepisauroids. 

 There are a number of exceptions to this generalization and the whole question of the position of the 

 pectoral fins will be more fully discussed in a separate section (pp. 325-28). 



Lastly, Regan (191 1) said that the Alepisauroidea had '. . .strong pointed canines in the lower jaw 

 and on the palatines'. This is true for his inclusions, Scopelarchus, Evermannella, Omosudis and 

 Alepisaurits and for Anotopterus, but this description does not cover certain of the paralepidids, such 

 as Paralepis and Magnisudis (Harry, 1953). However, there are certain features of dentition possessed 



