interoperculum 



mesopterygoic 



Figure 250.— Arothron 

 atellatus : lateral view of 

 head, 292 mm SL. India. 



hyomandibulor 

 proolk I pterotic 

 sphenottc /| 



Figure 251. —Tctroodonm6u: lateral 

 view of head, 47.7 mm SL, Congo. 



nteroperculum 



ectoplerygoi 



lively narrow; 3) the ethmoid and vomer are extremely 

 elongate; 4) the prefrontals are placed in about the mid- 

 dle of the skull; 5) the sphenotics form only the rear 

 margin of the orbit; and 6) the frontals are wide poste- 

 riorly over the skull but very narrow interorbitally and of 

 constantly decreasing width anteriorly. By comparison, 

 S. annuiatus has: 1) a broad skull and short wide snout 

 region; 2) the palatines are widely divergent and the jaws 



are relatively wide; 3) the ethmoid is of moderate length 

 and the dorsal surface of the vomer is exceptionally 

 short; 4) the prefrontals are placed anteriorly well in 

 front of the middle of the skull; 5) the sphenotics are 

 prolonged anterodorsally to form not only the rear but 

 also part of the dorsal margin of the orbit; 6) the frontals 

 are laterally expanded anteriorly to the extent that they 

 are wider anteriorly than posteriorly. 



