ESPECIALLY MYCTOPHOIDS 201 
(Text-fig. 64) resembles that of the basal myctophiforms (Aulopus, Text-fig. 93 and 
Sardimioides, Text-fig. 72) in the fusion of preural vertebra one and ural vertebra 
one. It has already been shown elsewhere that the same state of affairs exists in 
both the Cimolichthyoidei and the Enchodontoidei. This character then is of no 
real value in the understanding of relationships. It would appear that the consolida- 
tion of the caudal skeleton is general throughout the more basal Protacantho- 
pterygii, and the first step is the fusion of the first preural vertebra with the first 
ural vertebra. 
The nature of the neural components of preural vertebra two (the first free preural 
vertebra) is of interest. In the halecids the neural spine is complete in Hemisaunida 
but reduced in Halec. In the myctophiforms the neural spine is absent. This 
reduction and loss of the neural spine is probably an expression of the further 
reduction and consolidation of the caudal skeleton. The basal salmoniforms 
retain the neural spine on preural vertebra two and in this respect the halecoids 
are closer to the basal stock. 
The Halecoidei as a whole present a constellation of primitive and advanced 
characters. A similar state of affairs has already been shown in both the Cimo- 
lichthyoidei and the Enchodontoidei. These have been placed on a structural grade 
below that of the myctophiforms and acanthopterygians, due to several primitive 
characters. The evolutionary trends shown by the halecids agree with those already 
seen in the cimolichthyoids and enchodontoids and with those in the myctophiforms. 
These trends are those which align the group within the Protacanthopterygii (sensu 
Greenwood, et al., 1966), and can be summarized as follows : 
Tendency for premaxilla to exclude maxilla from the oral border. 
Tendency for supraorbital to be lost. 
Tendency for supramaxillae to be lost. 
Reduction in the roof of the post-temporal fossa. 
Tendency for pelvics to advance. 
Cre Sie hare 
Tendency for the caudal skeleton to become consolidated, the first step 
being the fusion of preural vertebra one with ural vertebra one. 
7. Tendency for the body to become shortened and deepened. 
Certain basic features, as opposed to trends, suggest that the halecoids are closest 
to the salmoniform grade at the base of the Protacanthopterygii. These would 
include the retention of a mesocoracoid arch ; absence of an ascending process on 
the premaxilla ; toothed maxilla ; supraorbital present ; numerous branchio- 
stegal rays ; finally the large number of pelvic rays. Following on from these 
considerations it is apparent that the halecoids are not directly related to any of the 
above mentioned groups (enchodontoids, cimolichthyoids, myctophiforms or 
acanthopterygians), but are related only in so far as they are contemporary descend- 
ants from an earlier stock within the Salmoniformes. 
