COLLETTE and RUSSO: SPANISH MACKERELS 



orly and the frontals and sphenotics laterally. 

 There is a space between the left and right 

 pterosphenoids opening into the brain chamber 

 just anterior to the basisphenoid. In most species 

 of Scomberomorus, there is an anterior medially 

 directed lobe on each pterosphenoid. These lobes 

 meet along the median line or at least come very 

 close to each other in adults of three species: 

 commerson (over 1,000 mm FL), caualla (over 550 

 mm FL), and lineolatus (over 750 mm FL). Small- 

 er specimens of these 3 species and all sizes of the 

 other 15 species have a wide gap or fenestra 

 between the left and right lobes. The gap is about 

 equal to the width of the parasphenoid or slightly 

 larger in three species: brasiliensis, koreanus 

 (Fig. 12a), and concolor (Fig. 12b). The gap is 

 largest in S. multiradiatus , so large that there is 

 virtually no medially directed lobe. This causes 

 the window into the brain chamber to be almost 

 rectangular in this species. 



Sclerotic. — The sclerotic bones consist of two 

 thickened semicircular segments connected by 

 cartilage on the inner lateral surface and by 

 corneal membranes on the outside. The inner rim 

 of the sclerotic bones appears elliptical externally 

 as in the bonitos (Collette and Chao 1975) and 

 Thunnus (e.g., T. atlanticus, de Sylva 1955:fig. 

 7). The sclerotic bones of Grammatorcynus are 

 relatively larger, thinner, and close to circular. In 

 Acanthocybium, the sclerotic bones are ellipti- 

 cal as in Scomberomorus, but they are heavier 

 and extend further medially. The only species of 

 Scomberomorus that appeared to differ from the 

 other species is S. sinensis. The sclerotics are 

 especially thick in this species and there is a 

 thick bony lump in the middle of the posterior 

 surface of one of the two sclerotics. Other species 

 of Scomberomorus have a thickening of the bone 

 in the same region but it does not form a distinct 

 protrusion as it does in S. sinensis. 



Basisphenoid. — The basisphenoid is a small, 

 median, Y-shaped bone that connects the para- 

 sphenoid, prootics, and pterosphenoids. The com- 

 pressed median vertical base bears an anterior 

 median process but lacks a posterior process as is 

 present in other scombrids such as Thunnus 

 (Gibbs and Collette 1967) and most bonitos (Col- 

 lette and Chao 1975). In most species of Scomber- 

 omorus there is at least a trace of a lateral ridge 

 that extends laterally and posteriorly on each 

 side of the anterior process. There is great varia- 

 tion in the length of the anterior process and in 



the relative degree of development of the lateral 

 ridges. Both features are best developed in S. 

 commerson where the length of the anterior pro- 

 cess is greater than the height of the vertical axis 

 of the bone. 



Infraorbitals. — The infraorbital (suborbital) 

 series of Scomberomorus consists of from 9 to 13 

 elements which enclose the infraorbital branch of 

 the lateral sensory canal system (Fig. 21a). Only 

 9 elements were observed in S. munroi, S. sierra, 

 and S. sinensis, but 13 elements were observed in 

 S. brasiliensis. The canal enters the infraorbital 

 series at what is usually considered the last 

 element (dermosphenotic) and continues around 

 the orbit to terminate on the first infraorbital 

 (lachrymal). 



The first infraorbital (lachrymal or IOl) is the 

 first and largest element in the infraorbital se- 

 ries. Anteriorly, several canal tubes open on the 

 laminar, platelike surface of the bone. Posterior- 

 ly, the canal tube continues directly to the second 

 infraorbital. The first infraorbital is an elongate 

 bone (length/height = 2.8-3.5) that covers part of 

 the maxilla and is attached to the lateral ethmoid 

 dorsally by a mesially directed articular process. 

 The anterior portion is forked with a thin ante- 

 rior process. This process is a point of attachment 

 for a ligament connected to the nasal. The projec- 

 tion is present in all species of Scomberomorus 

 except S. lineolatus and S. tritor. The portion 

 posterior to the articular process is elongate, 

 pointed, and longer than the anterior portion. 

 The general shape of the first infraorbital in 

 Scomberomorus is similar to that in the bonitos 

 (Collette and Chao 1975:fig. 28), particularly 

 Cybiosarda elegans, except that the anterior pro- 

 cess is smaller and more dorsally directed than in 

 Cybiosarda. Acanthocybium differs from Scom- 

 beromorus in having the posterior portion of the 

 first infraorbital short and broad, shorter than 

 the anterior portion (Fig. 21b). Grammatorcynus 

 has a feebly forked anterior end (Fig. 21c), lack- 

 ing a distinct anterior process such as is present 

 in Scomberomorus and Acanthocybium. 



As Devaraj (1977) noted, the dorsal margin 

 of the anterior part of the first infraorbital is 

 straight, or nearly so, in S. cavalla and S. com- 

 merson but clearly concave in the other species. 

 Mago Leccia (1958:pl. 4, fig. 7) indicated that S. 

 cavalla lacked the characteristic anterior projec- 

 tion, but we have found it to be present in our 

 material. In other respects, there seems to be as 

 much variation between individuals of a species 



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