ESPECIALLY MYCTOPHOIDS 197 
sauroids’. In both groups however the pelvics remain abdominal in position, and 
Marshall (1961 : 367) has indicated that the position of the pelvics in the myctophi- 
forms is correlated with the mode of life, rather than being correlated with locomotion 
as in the Acanthopterygii, the bathypelagic myctophiforms having in general 
abdominal pelvics, whilst the benthonic groups have sub-thoracic pelvics. This 
assumption substantiates one aspect concerned with the division of the enchodon- 
toids into pelagic and benthonic families since the Enchodontidae with abdominal 
pelvics were probably pelagic whilst the Eurypholidae with sub-thoracic pelvics 
were benthonic. 
The caudal skeleton is very similar to that of the cimolichthyoids. The tails 
of Enchodus (Text-fig. 42) and Eurypholis (Text-fig. 48) are remarkably alike and 
show features which duplicate those seen in Sardinioides (Text-fig. 72) and Aulopus 
(Text-fig. 93) among the Myctophiformes, and Pvionolepis in the Cimolichthyoidei. 
These features include : 
1. The fusion of preural vertebra one with ural vertebra one, the compound 
centrum so produced supporting a stegural. 
2. The second ural vertebra present as a terminal half-centrum supporting four 
upper hypurals. 
3. Preural vertebra two has no neural spine, simply an expanded neural arch. 
The absence of basal fulcral scales above and below the caudal peduncle in the 
enchodontoids is as in Prionolepis. Both Sardinioides and Aulopus possess fulcral 
scales and are thus on a more primitive level in respect of caudal structure than the 
enchodontoids. 
The squamation of the Enchodontoidei is greatly reduced as it is in the ‘ alepi- 
sauroids ’. This reduction is no doubt correlated with a distensible stomach (as in 
the Cimolichthyoidei, p. 191). 
In conclusion then, the suborder Enchodontoidei has two families of divergent 
habitat. The order Myctophiformes, likewise, is frequently divided into two main 
groups, and as Gosline, Marshall and Mead (1966 : 6) have pointed out the anatomical 
differences between the two groups may reflect differences in environment as much 
as in ancestry. These authors tentatively suggest that the Myctophiformes was 
originally a benthonic group and cite the presence of a sensory canal commissure 
across the frontals as evidence. In Eurypholis a median dorsal sensory canal is 
present behind the occiput and probably served the same function. The only other 
character which the Eurypholidae possess which is not present in the Enchodontidae 
is a roof to the post-temporal fossa. This fact would tend to indicate that the 
Eurypholidae is the more primitive of the two, but in most other respects the 
Eurypholidae show specializations suiting them to a benthonic existence. Thus the 
Enchodontoidei are best looked on as being derived probably from a pelagic ancestral 
stock within the Salmoniformes which evolved to produce a benthonic group as well 
as retaining its original pelagic habit. 
