FISHES OF FAMILY BLENNIIDAE 21 



posterolaterally on each side, the basioccipital joins the ventral sur- 

 face of each exoccipital. Dorso-anteriorly the basioccipital joins the 

 posteroventral surface of the prootic. The dorsoposterior surface of 

 the basioccipital forms the floor of the foramen magnum. 



Frontal (figs. 1-4). — The frontals are relatively long and large 

 bones each consisting of a narrow, anterior arched portion and a 

 posterior broad portion. They are joined to each other for their entire 

 length. Along the longitudinal midline of the dorsal surface of the 

 skull they narrowly and irregularly overlap each other; posteriorly 

 their median edges are raised dorsally and form a low, thin crest, 

 highest at its posterior end. The crest terminates at the large mid- 

 dorsal opening of the supratemporal branch of the laterosensory canal 

 system (the external, cutaneous openings, pores — termed "predorsal 

 commissural pores" by Springer, 1967b — are extensions of this single 

 opening). 



The dorsoposteriormost portion of the crest of each frontal impinges 

 on its respective side on the lateral surface of the raised, anterior 

 extension of the supraoccipital (not visible externally). 



The dorsoposterior end of each frontal hes under the dorso-anterior 

 end of its respective parietal but may form a pocket into which the 

 end of the parietal inserts. At the externally visible anteriormost ex- 

 tension of its respective parietal, each frontal abruptly passes external 

 to the ventroanterior portion of the parietal and continues ventrally 

 external to the dorso-anterior end of its respective pterotic, the dorso- 

 anterior end of its respective sphenotic, and the dorsoposterior end 

 of its respective pterosphenoid. 



Each frontal has a lateroventral descending wing, the ventral por- 

 tion of which meets and lies internal to the dorsoposterior portion of 

 the ascending wing of the parasphenoid on its respective side, but 

 external to the dorso-anterior portion of its respective pterosphenoid. 



The sensory canal (supraorbital) in the frontal extends through the 

 anterior arch of the frontal and along the lateral margin of the bone. 

 The anterior opening of the canal is continuous with the dorsal open- 

 ing of the sensory canal of the nasal bone. At a point just anterior to 

 where the arched and broad portions of the frontal meet (above the 

 orbits), each frontal is pierced medially by a foramen that leads to 

 its sensory canal, thus forming a common connection between the 

 two supraorbital canals. This common connection also opens to the 

 surface of the skull by a foramen between the frontals (haK the mar- 

 gin of this foramen formed by each frontal). There are several openings 

 to the supraorbital canal in the region above the orbit. The most 

 posterior of these openings is at the junction with the dorsal opening 

 of the infraorbital canal in the fifth circumorbital (dermosphenotic) 

 bone. The supratemporal canal continues posteriorly from the orbital 



