COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



Figure 28.-Larchrymals of six species of Sardini, left lateral view. a. Cybiosarda elegans, New South Wales, 360 mm FL. b. 

 Orcynopsis unicolor, Tunisia, 495 mm FL. c. Sarda orientalis, Tokyo, 350 mm FL. d. Sarda sarda, Tunisia, 504 mm FL. e. 

 Gymnosarda unicolor, Truk Islands, 772 mm FL. f. Allothunnusfallai, California, 680 mm FL. a, b, and c drawn twice as large 

 as d, e, and f . 



elongate in Allothunnus and the species of Sarda 

 (also see vomer). In ventral view, the general 

 characteristic of the parasphenoid is a gradual 

 narrowing of the bone from anterior to posterior. 

 Orcynopsis has the widest and strongest 

 parasphenoid; species of Sarda have the weakest. 

 Broad parasphenoids are also present in 

 Scomberomorus and Acanthocyhium; narrower 

 parasphenoids in Auxis, Euthynnus, Katsuwonus, 

 and Thunnus. The broadest portion of the 

 parasphenoid is usually located at or before the tip 

 of the V-shaped joint with the vomer in all bonitos 

 except Allothunnus. In five skulls (406-778 mm 

 FL) of Allothunnus, the broadest portion of the 

 parasphenoid is in the posterior half of the bone, 

 about at the beginning of the ventral keel. This is 

 in contradiction to Nakamura and Mori (1966, fig. 

 4B), whose illustration of a specimen (876 mm FL) 

 shows the parasphenoid as similar to other bonitos. 

 The anterior edge of the lateral wings of the 

 parsphenoid is smoothly concave forward and 

 forms a dorsolaterally directed shelf, visible ven- 

 trally in all bonitos except Allothunnus. In 

 Allothunnus (Figure 19), the anterior edge of the 

 lateral wing is deeply concave and the wing 

 projects vertically along the prootic wing toward 

 the roof of the skull, as in the more advanced 

 scombrids. The posterior opening, between the 

 lateral flanges of the parasphenoid, is usually 

 elongate and the lateral flange does not extend 

 beyond the juncture of the skull with the first 

 centrum (Figures 15-19). In our Gymnosarda 

 skulls, this opening is much smaller than in the 

 other bonitos (Figure 17). A thin layer of bone 

 covers the anterior portion of the opening, perhaps 



indicating additional ossification in larger in- 

 dividuals of this particular species. 



In lateral view (Figures 20-24), the 

 parasphenoid forms the ventral border of the orbit 

 and connects with the lateral ethmoid, 

 basisphenoid, prootic, and basioccipital bones dor- 

 sally. The ventral keel projects further ventrally in 

 Gymnosarda and Allothunnus than in Orcynopsis 

 and Cybiosarda. The posterior one-third of the 

 parasphenoid and its lateral flanges are strongly 

 convex in Allothunnus, forming the unique 

 posteroventral outline of its skull (Figure 24). A 

 middorsal ridge is also present in all bonitos. This 

 ridge arises from the juncture of the lateral eth- 

 moids, where the ridge projects the most, and 

 merges into the main axis of the parasphenoid 

 posteriorly at about the beginning of the ventral 

 keel. Usually, a triangular piece of cartilage, con- 

 necting with the lateral ethmoid, covers the most 

 anterior end of the dorsal ridge. The middorsal 

 ridge is least prominent in Cybiosarda. 



Basioccipital. -The basioccipital is the most 

 posteroventrally located bone of the skull. It is 

 shaped like an inverted U with lateral flanges on 

 either side of the skull and forms the roof and 

 lateral walls of the posterior myodome. Anteriorly, 

 the basioccipital is attached to the prootic bones 

 and dorsally with the exoccipital bones. Its lateral 

 flanges expand ventrally to meet the flat posterior 

 flanges of the parasphenoid. Posteriorly, the 

 lateral flanges fuse to form a circular margin in a 

 slightly backward oblique position and attach to 

 the margin of the first vertebral centrum (Figure 

 25). In lateral view, a distinct deep concave pit is 



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