Figure 271 .—Dorsal view of skull o( Ephippion 

 guttifer, 101 mm SL, Guinea. 



is at least moderately arched, with the anterolateral end 

 of the prefrontals curved down in front of the eye, more so 

 in adults than in the young, and enclosing the olfactory 

 foramen, and the ethmoid of moderate to narrow width 

 (less wide than in Tetraodon and Ephippion but no less 

 wide than in Chelonodon, Carinotetraodon, and most 

 species of Monotreta). 



Not all of these typical features are confined to Aroth- 

 ron, for the prefrontal entirely encloses the olfactory fo- 

 ramen in the related Ephippion and in Chelonodon 

 patoca (but not C. fluviatilis), while in the related Tetra- 

 odon lineatus (but not T. mbu) the prefrontal encloses all 

 but the medial edge of a large olfactory foramen. The fo- 

 ramen completely encloses the prefrontal in several spe- 

 cies of the more distantly related genera Amblyrhyn- 

 chotes, Torquigener, and Fugu, although in none of these 

 do the prefrontals have such large downcurved antero- 

 lateral regions as found in most adult Arothron. The 

 sphenotics are not laterally expanded beyond the fron- 

 tals in Monotreta gularis, and are only slightly to mod- 

 erately expanded beyond them in the other species of 

 Monotreta. 



Moreover, one species, originally described as Tetrao- 

 don armilla McCuUoch, that has the general external 

 configuration and look of an Arothron, including a single 

 lateral line, differs greatly from the typical Arothron 

 skull plan. Externally, armilla differs from Arothron in 

 having the nasal apparatus represented by a single flap 

 of skin on each side of the head, the outer surface smooth 

 and the inner only very slightly irregular, while in Aroth- 

 ron there is always a bifid tentacle whose inner surfaces 

 are pitted by circular olfactory organs. 



In the three typical species of Arothron studied {hispi- 

 dus, nigropunctatus, stellatus), the parasphenoid either 

 does not have a dorsal flange in the orbit, or does not 

 have it well enough developed to reach dorsally far 

 enough to contact the frontals, while in armilla the dor- 

 sal flange is well developed and contacts the prefrontals 

 as well as the frontals. While the typical species of Aroth- 

 ron have minute teeth on the first pharyngobranchial, in 

 armilla they are relatively well developed, being only 

 slightly smaller than those of the second and third 

 pharyngobranchials. In typical Arothron there is little or 

 no evidence of prootic prongs in the rear of the orbit 

 representing the remains of the dorsal roof of the myo- 

 dome, while the prootic prongs are well developed in ar- 

 milla, reaching almost to the midline. In typical Aroth- 

 ron several trituration teeth are present in a single series 

 to either side of the midline of the upper jaw, but none 

 are present in the lower jaw, while in armilla, even at the 

 small size of the examined individual, the numerous tri- 

 turation teeth in both the upper and lower jaws are con- 

 solidated into large composite plates to either side of the 

 midline. Like the typical species o( Arothron, armilla has 

 only a ventral hypohyal and no interhyal. 



The most dramatic and perhaps phylogenetically in- 

 teresting way, however, in which armilla differs from 

 typical Arothron is in the shape of the frontals and pre- 

 frontals. Instead of having the frontals greatly laterally 

 expanded above the orbit, as in typical Arothron, the 

 frontals of armilla are only slightly wider over the rear of 

 the orbit than more posteriorly, and gradually and evenly 

 taper to bluntly rounded ends anteriorly, much as in 

 most of the more generalized species of genera with two 

 nostrils. The prefrontals of armilla are not enlarged and 

 laterally expanded to the same degree as the frontals at 

 the rear of the orbit, and, although they do completely 

 enclose the olfactory foramen, they are only slightly 

 downcurved anterolaterally. The prefrontals in armilla 

 are separated from one another about half and half by 

 the ethmoid and frontals, a probably more generalized 

 condition than having them separated mostly by the eth- 

 moid as in typical Arothron. 



Although in two features (a single nasal flap and a dor- 

 sal flange of the parasphenoid meeting the frontals) ar- 

 milla is more specialized than the typical species of 

 Arothron, it has a far more generalized condition of skull 

 configuration, especially of the frontals and prefrontals. 

 In fact, if the several species of Arothron not examined 

 for this work have skull structures similar to that of the 

 three typical species examined here and not intermedi- 

 ate between them and armilla, then armilla may be con- 



