190 UPPER CRETACEOUS TELEOSTS 
the caudal skeleton in the Cimolichthyoidei, as represented by Prionolepis, is 
practically identical to that of the Cretaceous myctophiform Sardinioides (Text-fig. 
72) and the Recent Aulopus (Text-fig. 93). In both the Cimolichthyoidei and the 
basal myctophiforms the first preural vertebra is fused with the first ural vertebra ; 
ural vertebra two is present as a small half-centrum supporting hypurals 3, 4, 5 and 6 ; 
a stegural is formed from uroneural one and the neural arches of ural vertebra one and 
preural vertebra one ; the neural spine of preural vertebra two is reduced so that only 
an expanded neural arch occurs. However a primitive feature of the myctophiform 
tail is the presence of basal fulcral scales both above and below the peduncle, these 
are absent in the cimolichthyoids. Apart from the tail other comparative points 
can be made between the cimolichthyoids and the more advanced ‘ alepisauroid ’ 
myctophiforms. For instance the parietals are separated by the small supra- 
occipital in both groups. Nasal bones are absent in the cimolichthyoids, either 
having been lost, or more likely incorporated into the mesethmoid as a result of the 
lengthening of the rostrum. This fusion of the nasal with the mesethmoid also 
occurs in several advanced myctophiforms, e.g. Lestidium, Anotopterus, Alepisaurus 
(Parr, 1929 : 28, 34). Further the cimolichthyoid jaw resembles that seen in the 
‘ alepisauroid ’ myctophiforms, except for the exclusion of the maxilla from the gape 
in the latter. In the cimolichthyoids (Text-fig. 21) the premaxilla does extend back 
for a considerable length below the maxilla, but never has an ascending or an articular 
process. The maxilla is reduced to a narrow strut of bone entering the gape poster- 
iorly, and never has articulatory head processes. In Alepisaurus (Text-fig. 79) on 
the other hand, the upper jaw, although at first sight simple and similar to that of 
the cimolichthyoids, has been derived from a much more complex condition. In the 
earlier myctophiforms the premaxilla possessed an articular and an ascending 
process, while the maxilla had a differentiated head and supported two supra- 
maxillae. As a result of specialization the articular process and the supramaxillae 
have been lost and the maxillary head is simplified. As in the cimolichthyoids this 
specialization is concerned with the lengthening of the rostral region. Other than 
this the cimolichthyoids still bear teeth on the vomer and the endopterygoids 
whereas in the advanced ‘ alepisaurs ’ these teeth have been lost. 
In the cimolichthyoids barbed teeth occur on the palate and the ectopterygoid 
(Text-fig. 20) and serve to increase the total cutting edge of the teeth. Similar 
teeth are seen on the glossohyal (tongue) of Scopelarchus, but not elsewhere in any 
other myctophiform (Parr, 1929). 
No traces of an interoperculum have been found in the cimolichthyoids. This 
feature is difficult to account for but might in some measure be due to the retention 
of an upright suspensorium, since the interoperculum is often small in forms with a 
vertical preoperculum. In Alepisaurus (Text-fig. 79) and Omosudis the suspen- 
sorium is upright and the interoperculum minute, possibly indicating a stage in the 
disappearance of this bone. 
The transverse processes in the dercetids project strongly in a lateral direction, 
while Synodus among the recent myctophiforms has transverse processes which 
project ventrally. Two pairs of transverse processes are present on each centrum in 
