ESPECIALLY MYCTOPHOIDS 189 
Gregory (1933 : 201) placed the dercetids in the Heteromi but stated that any 
similarities with the notacanths must be put down to convergence. Authors since 
that time (Berg, 1940 ; Bertin & Arambourg, 1958 ; Romer, 1966) have retained 
the Dercetidae within the Myctophiformes following Regan’s (1911) tentative 
proposals. 
The association of the dercetids with the notacanths is obviously incorrect due to 
several basic dissimilarities, for example the complete regression of the caudal fin 
skeleton, the small inferior mouth and the snubbed rostrum of the notacanths are 
vastly different to those of the dercetids. Greenwood ef al. (1966) have placed the 
notacanths in the Elopomorpha, and following Arambourg (1954) placed the 
Dercetidae in the myctophiforms. 
The Cimolichthyoidei would appear not to be related to the myctophiforms 
because of certain primitive features which are not seen in the basal myctophiform 
stock, for instance, the absence of an ascending process and the toothed maxilla 
with no supramaxillae. 
The Cimolichthyoidei as a group were relatively numerous, especially the smaller 
dercetids, and extended throughout the Upper Cretaceous (except for the Maastrich- 
tian). The first genus to appear in the fossil record is the advanced Rhyncho- 
dercetis, in the Lower Cenomanian. The less advanced genera Cimolichthys and 
Dercetis do not appear in the record until the Upper Cenomanian. Thus the small 
cimolichthyoid radiation must have originated within the Lower Cretaceous. The 
advanced characteristics shown by the group exclude them from having given rise 
to any other salmoniform. These advanced characteristics are as follows : 
Parietals separated in the mid-line. 
Orbitosphenoid, basisphenoid and antorbital absent. 
Interoperculum absent. 
Reduced squamation. 
Abnormal transverse processes and lengthened centra. 
Overall snout and body elongation. 
SE ee 
Several of these advanced features also preclude the cimolichthyoids from having 
given rise to the Myctophiformes. The Cimolichthyoidei also retain many primitive 
characters in common with other members of the Salmoniformes such as : 
1. Partially or completely roofed post-temporal fossa. 
Maxilla enters the gape and is toothed. 
No ascending process on the premaxilla. 
Supratemporal present. 
Teeth on vomer and endopterygoid. 
Supraorbital present. 
Complex trigemino-facialis chamber. 
Abdominal pelvic fins. 
g. Epineurals in abundance. 
CONS ea oats 
Despite the fact that the cimolichthyoids are in no way related to the myctophi- 
forms the two groups show a considerable degree of parallel evolution. For example 
