GREGORY: FISH SKULLS 



245 



On the lateral surface of the otic region there is a notable absence in Luciolates of the 

 deep fossa which in the tarpon and other isospondyls lodged a diverticulum of the swim- 

 bladder. The fossa for the dilatator operculi muscle, which in the tarpon is conspicuous 

 above the postorbital process of the sphenotic, must be represented in Luciolates by the 

 very narrow, nearly horizontal fossa chiefly on the lateral border of the pterotic immediately 

 above the elongate glenoid cavity of the hyomandibular. The bony brain-trough in front 



antveTT.oonal 



derm art 



Roccus lineatus 



Fig. 119. Roccus lineatus. 



A. Right half of skull and pectoral girdle, showing the suspension of the jaws and pectoral girdle from the neurocranium. 

 . Right half of neurocranium, medial view, showing ethmo-vomer block, keel bone [pas], interorbital bridge and cranial vault. 



B. Right 



of the sphenotie in Luciolates is notably reduced and lightened by the complete elimination 

 of the orbitosphenoid, while the strut from the Y-shaped basisphenoid that comes down to 

 rest on the parasphenoid is here notably weak, so that the parasphenoid, the frontals and 

 the otic bones carry all the load. However in Roccus (Fig. 119^) the basisphenoid is still 

 iluable brace, while the parasphenoid has a strong anterior ascending fork. 



a vai 



