228 UPPERS CRELACEOUS LELEOSTIS 
genus, Chlorophthalmus, although somewhat more advanced than Awlopus is still little 
different from Sardinioides. The remainder of the recent forms are much more 
specialized, particularly for life in deeper waters. Harry (1953 : 244) has identified 
paralepidids in the Miocene of California. These are somewhat more advanced than 
Chlorophthalmus, and are on the line which culminates in the present day Anotopterus 
and Lestidium. Arambourg (1925) has described a Miocene myctophoid fauna from 
Licata in Sicily, and his specimens are closely related to the present day Myctophidae. 
The Californian Miocene deposits certainly seem to be deep water (Crane, 1966 : 20), 
as do the Sicilian ones. 
The colonization of a deep sea environment has been considered by Marshall 
(1963 : 189) who stated that radiation into the central water masses would have been 
from a relatively rich to a poor food producing area. The cause of this migration 
into deeper water can be accounted for if the factor of competition is considered. 
During the Upper Cretaceous the beryciforms and subsequently the perciforms 
were radiating and occupying many niches already occupied by salmoniforms 
and myctophiforms. The acanthopterygians with their more versatile jaw structure, 
their increased manouevrability and the development of protective mechanisms 
as well as offensive mechanisms on both fins and scales seem to have provided 
overwhelming competition for many groups. The Myctophiformes, however, 
seem to have had sufficient evolutionary plasticity to become adapted to a new 
environment, that of deeper water. Thus the myctophiforms were able to develop 
phosphorescent organs, increase the size of the gape, lose the air bladder and 
decrease the amount of ossification and squamation. Together with these particular 
specializations the myctophiforms show other trends which are present in the fossil 
salmoniforms, e.g. enchodontoids and halecoids, and which mirror features seen 
throughout the Acanthopterygu. These include the loss of the orbitosphenoid, 
basisphenoid, antorbital and supraorbital ; the separation of the parietals ; the 
loss of supramaxillae, and finally the loss of the roof to the post-temporal fossa. In 
the myctophiforms this reduction is obviously useful in that it reduces the density of 
the body, but this effect would appear to be only a secondary one. Throughout the 
Protacanthopterygii and Acanthopterygii, irrespective of habitat and mode of life, 
the more advanced and specialized members undergo these reductions. 
In a discussion of the Myctophiformes some consideration must be given to the 
Paracanthopterygii of Greenwood, et al. (1966). This group represents a parallel 
spiny-finned radiation to the Acanthopterygii and contains the percopsiforms, 
batrachoidids, lophioids, ceratioids and gadoids. Greenwood, et al. (1966 : 371) 
proposed that this group might have been derived from some Cretaceous myctophi- 
form such as Sardinioides. They tentatively proposed that a ‘ paraberycoid ’ 
radiation might have occurred, this hypothetical radiation being distinct from the 
berycoids and the two being independently derived from the Salmoniformes. It is 
quite possible that the paracanthopterygians represent forms which arose from the 
myctophiform lineage at about the time that the beryciforms arose. Some degree 
of substantiation for the alignment of the paracanthopterygians with the myctophi- 
forms is the presence of an adipose fin in both groups. The adipose fin is not 
