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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



and modified into powerful electric organs (White, 1918). These newly-evolved organs are 

 evidently responsible for the presence of the very large postorbital vacuities with which 

 the orbits are confluent. Their presence has also caused the extreme constriction of the 

 frontals and the approximation of the side walls of the deep groove above the ethmoid, 

 the fore part of which receives the ascending processes of the premaxillae. The electric 

 organs evidently press posteriorly against the braincase, which is excessively short and wide. 



scap 



Astroscopus sp 



AstrosGopus y-^raecum 



Fig. 247. Astroscopus. 



The front walls of the braincase are formed from ascending flanges of the parasphenoid 

 as they meet descending flanges from the frontals. With the dorsal shifting of the eye- 

 muscles and their derivatives, the primitive eye-muscle canal beneath the floor of the brain- 

 case has been abandoned and closed up, so that the systematists report "no myodome" as 

 characteristic of this superfamily. The lack of a myodome in turn probably conditions 

 the fact that the parasphenoid lacks the normal posterior extension beneath the braincase. 



The electric organs extend so far posteriorly that only an antero-posteriorly short and 

 transversely very wide and flat cranial roof is left, consisting of conjoined frontals, followed 

 by small flat parietals which seem to have joined secondarily above the small supra- 

 occipital. The occipital border of the skull roof is formed by a transverse row of small 

 "neuromastic" or lateral line bones, apparently representing respectively the "scale bones" 

 (extrascapulars), the posttemporals and the supracleithra. The suborbital plates, along 

 with the dorsally displaced eyes and related parts, have likewise moved upward to form the 

 outer border of the upward-looking face. Together they form a stiff armor for the cheek 

 and one of them (the third) is supported by a special process of the hyomandibular, just in 

 front of the top of the preopercular. This third suborbital is excluded from the border of the 

 orbit and, being also braced posteriorly by the preopercular (through the special process 

 mentioned above), the arrangement is suggestive of certain of the mail-cheeked fishes. 



