406 
PACIFIC SCIENCE, Vol. XX, October 1966 
of gill arch and other sructures may be divided 
into two subfamilies, one of which is pro- 
posed as new, Uropterygiinae and Muraeninae. 
The arches of Sen worrier are sufficiently similar 
to those of Anguilla to suggest a relationship 
between these forms. Those of nemichthyids 
are somewhat reduced ( Nemichthys , Avocet- 
tina ) or severely reduced ( Cyema ). 
4. The members of the synaphobranchoid 
lineage are alike in having the third hypobran- 
chials posteriorly directed. 
5. Within the congroid lineage most of the 
members have a well ossified and complete gill 
arch skeleton. The only major exceptions are 
found among the Ophichthidae, whose members 
show great variability in gill arch structure. 
6. Gill arch modifications seem related to 
body form and habits of eels. The gills are 
posteriorly displaced in the more elongate 
forms. Loss of skeletal elements has resulted 
in many eels in a highly expandible pharynx, 
seemingly an adaptation for swallowing large 
prey. The development of "pharyngeal jaws" 
in the more highly specialized eels seems related 
to mechanical problems of moving relatively 
large prey through a secondarily elongate 
pharynx. 
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