198 UPPER CRETACEOUS TELEOSTS 
(D) Suborder HALECOIDEI 
Three quite closely related genera, Halec, Phylactocephalus and Hemisaurida are 
included in this new suborder. There is a closer affinity between Halec and 
Phylactocephalus than between either of these and Hemisaurida. 
Halec has a relatively shallow head and body with certain advanced characteristics, 
particularly in respect of the neurocranium. These features are : 
1. Unroofed post-temporal fossa. 
Parietals separated in the mid-line. 
No basisphenoid. 
No orbitosphenoid. 
No supratemporal. 
Simplified trigemino-facialis chamber. 
DAR WD 
All of these features are normally associated with advances encountered in the 
acanthopterygian grade (Patterson, 1964). The more primitive features seen in the 
genus are concerned with the body and are as follows : 
1. Pectoral girdle with mesocoracoid arch. 
2. Abdominal pelvic fins. 
3. Incompletely fused vertebral elements. 
4. Numerous intermuscular bones. 
The genus Phylactocephalus agrees with Halec in respect of the skull structure, but 
exhibits several more advanced features associated with the body. For example, 
the body is shortened (33 vertebrae, whereas Halec has 40 to 45), and the depth of 
both head and body are considerably greater than in Halec. Correlated with body 
shortening is the relative position of the fins, the dorsal having advanced and the 
pelvics having migrated to practically a sub-thoracic position. This migration may, 
however, merely be a further expression of the overall body shortening, rather than 
a major morphological, and presumably functional migration, since the pectorals 
still remain low down on the body. Also the pectoral girdle of Phylactocephalus may 
still retain the mesocoracoid arch present in Halec eupterygius (Text-fig. 62). 
Another character possibly associated with this general shortening and deepening of 
the body is the decrease in the number of branchiostegal rays (Phylactocephalus has 
10, whereas Halec has 15 or 16). 
Possibly these more advanced features which Phylactocephalus possesses indicate 
a different mode of life. Halec could have been benthonic and provided a stock from 
which a more active pelagic form such as Phylactocephalus was derived. Indications 
of a bottom-dwelling habit are given by the inflection of the lower edge of the 
mandible (already noticed in the probably benthonic Eurypholis, p. 193) and the 
high number of branchiostegal rays in Halec. In Phylactocephalus the number 
of rays is reduced to ten but the jaw still shows signs of being inflected. The 
overall body shape of Halec suggests certain recent benthonic forms such as 
Synodus. However Synodus has sub-thoracic pelvics which Marshall (1961 : 368) 
suggests are used together with the tail as props. Although Phylactocephalus has 
sub-thoracic pelvics, from its shortened, deepened, laterally compressed body it is 
