200 UPPERVCREDACEOUSSLELEOSES 
Little mention has been made in the past of the relationships and systematic 
position of the halecoids. Agassiz (1834) first used the generic name Halec, and also 
erected the family Halecidae, which he used to include the ‘ herring-like ’ fishes, the 
clupeoids and salmonoids of Cuvier. Pictet (1850) and Davis (1887) retained the 
family, Davis adding the genus Phylactocephalus. Woodward (1901) retained the 
generic name Halec (including Phylactocephalus Davis in its synonymy), but put it 
in the family Enchodontidae, where it has remained to the present day (Bertin & 
Arambourg, 1958 ; Romer, 1966). 
Gregory (1933 : 204) mentioned the genus Halec in connection with the Enchodon- 
tidae, but pointed out that Halec was on a slightly lower level than Enchodus in that 
it possessed well developed maxillary teeth. 
Woodward (1901 : 270) also mentioned Hemisaurida as an imperfectly defined 
genus which perhaps belonged in the family Scopelidae. Romer (1966) followed 
Woodward, but definitely assigned Hemisaurida to the family Myctophidae. 
Direct relationship with the enchodontoids as constituted in this work can be 
dismissed because of the following features shown by the Halecidae : 
1. Elongate palatine with two rows of teeth. 
2. No fenestrated premaxillary pedicel. 
3. Supraorbital bone present. 
4. Supramaxilla present. 
5. Mesocoracoid arch present. 
Certain similarities seen in the two groups appear to be the result of convergent 
modes of life, and possibly similarities in evolutionary potential. These are as 
follows : 
1. A similar neurocranial structure in the loss and reduction of certain 
bones (orbitosphenoid, basisphenoid, etc.). 
2. Reduction in squamation. 
3. Trend towards body deepening and shortening. 
4. Trend towards snout elongation. 
5. Trend for forward migration of the pelvic fins. 
The Halecoidei are also in no way related to the Myctophiformes. The incomplete 
exclusion of the maxilla from the gape, and the absence of ascending and articular 
processes on the premaxilla completely exclude the halecoids from any connection 
with the myctophiforms. 
The halecoids do, however, show some points of similarity with the myctophiforms 
which are possibly correlated with convergent and/or parallel evolution, in space as 
well as time. The halecids occur throughout most of the Upper Cretaceous (Ceno- 
manian, Turonian and Senonian), and this occurrence coincides with the initial 
radiation of the myctophiforms. Both groups appear to have inhabited similar 
environments (occurring as fossils at the same horizons), and identical evolutionary 
forces presumably would have acted upon them. Further, since they were probably 
derived from a common ancestral stock within the Lower Cretaceous, it is not 
surprising that some similarities should exist. For example the caudal skeleton 
