COLLETTE and RUSSO: SPANISH MACKERELS 



through about the seventh elements may be ex- 

 panded laterally as laminar plates which cover 

 the anterior end of the cheek scales. There may 

 be 10-16 rows of specialized cheek scales posterior 

 to the infraorbitals. These scales originate mesial 

 to the infraorbital canal tubes and extend poste- 

 riorly as flat, sometimes pointed, platelike ele- 

 ments. These platelike scales may themselves be 

 covered with more typical cycloid scales and 

 exhibit the same morphology as the corselet 

 scales of higher scombrids. The cheek scales of 

 Scomberomorus may represent the primitive 

 condition of the corselet. 



OTIC REGION.— This region encloses the otic 

 chamber inside the skull, and is formed by the 

 parietal, epiotic, supraoccipital, prootic, pterotic, 

 sphenotic, and intercalar (opisthotic) bones. 



Parietals. — The parietals articulate with the 

 frontals anteriorly, the supraoccipital mesially 

 and the pterotics laterally, sphenotics ventrally, 

 and epiotics posteriorly. The inner lateral crest 

 that originates at the middle of the frontal bones 

 continues through the parietals to terminate at 

 the epiotics. This crest is typical of scombrids and 

 is particularly well developed in Scomberomorus. 

 These crests originate on the parietals, instead of 

 the frontals, in Acanthocybium and Grammator- 

 cynus and are not as high as in Scomberomorus. 

 The parietals of all the species of Scomberomorus 

 are similar. 



There is a gap or fenestra on the dorsal surface 

 of the skull where the parietal, epiotic, and pter- 

 otic bones come together. It varies in shape from 

 roughly triangular to rectangular in most spe- 

 cies. There is wide variation from specimen to 

 specimen that tends to obscure potential inter- 

 specific differences. The gap is very small in some 

 specimens of eight species: commerson , concolor 

 (Fig. 12b), koreanus (Fig. 12a), maculatus , mun- 

 roi (Fig. lib), plurilineatus , queenslandicus , and 

 sierra. It is usually larger in the other species 

 and in most specimens of S. commerson (Fig. 

 11a). 



Epiotics. — The epiotics are massive, irregular, 

 and bounded by the parietals anteriorly, the 

 supraoccipital mesially, the exoccipitals posteri- 

 orly, and the pterotics laterally. The inner lateral 

 crests terminate at the posterior end of the epi- 

 otics. The medial process of the posttemporal 

 bone attaches here on a rough process. There are 

 slight differences between the species of Scom- 



beromorus in the attitude of the attachment area 

 and its roughness. In many species, the lateral 

 crest continues posteriorly almost perpendicular 

 to the skull. In some species such as S. commer- 

 son (Fig. 11a) and S. queenslandicus, the area of 

 attachment is flatter. This area is flat and rough 

 in Acanthocybium (Fig. 13a) and forms a separate 

 process in Grammatorcynus (Fig. 13b). 



Supraoccipital. — The supraoccipital forms the 

 dorsomedial portion of the posterior end of the 

 neurocranium and bears a well-developed crest 

 which continues anteriorly on the frontals and is 

 pronounced posteriorly as a strong supraoccipital 

 crest. The supraoccipital can be divided into two 

 parts: a thin, elongate triangular crest and a 

 roughly hexagonal base. The crest extends down 

 over the exoccipitals along the median line where 

 the dorsal walls of the exoccipitals suture with 

 each other, but it is not interposed between the 

 exoccipitals. The hexagonal base is bounded an- 

 teriorly by the frontals and laterally by the 

 parietals and epiotics. The crest extends posteri- 

 orly over the first vertebral centrum usually to a 

 level past the posterior margin of the centrum 

 (Figs. 14-16). The height of the crest varies among 

 species of Scomberomorus and is highest in three 

 species, S. guttatus, S. koreanus (Fig. 15a), and 

 S. multiradiatus. Dividing the height of the su- 

 praoccipital crest (ventral margin of supraoccipital 

 to edge of crest) by skull length (tip of vomer to 

 posteroventral margin of basioccipital) gives a 

 ratio of 0.46-0.57 for these three species, com- 

 pared with 0.34-0.45 in the other 15 species. Low 

 ratios are found in S. cavalla and S. commerson 

 (0.35-0.40) and in all six species of the regalis 

 group (0.34-0.42). 



Prootics. — In ventral view, the prootics con- 

 nect with all bones on the ventral side of the skull 

 which compose the posterior part of the neuro- 

 cranium (Figs. 17-19). Each prootic is bordered 

 ventrally by the parasphenoid; posteriorly by the 

 basioccipital, exoccipital, and intercalar; lateral- 

 ly by the pterotic and sphenotic; and anteriorly 

 by the pterosphenoid and basisphenoid. The pro- 

 otic bones are irregular in shape and meet each 

 other along the ventromedian line of the brain 

 case to form the anterior portion of the poste- 

 rior myodome. On the ventral surface, extending 

 from the lateral wing of the parasphenoid to the 

 sphenotic, the prootic forms a thick bridge which 

 strengthens the trigemino-facialis chamber (Allis 

 1903). A prootic foramen is present anterolateral - 



573 



