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



Gymnosarda has a comparatively deep notch but 

 the dorsally projecting process points more 

 anteriorly than in any other bonito (Figure 60g). 

 There is only a slight notch in Cybiosarda and no 

 indentation at all on the anterodorsal edge of the 

 bone in Orcynopsis. A ridge extends along the 

 length of the inner surface of the supracleithrum. 

 The ridge gradually merges into the main body of 

 the bone dorsally. It stops abruptly about two- 

 thirds of the way toward the dorsally projecting 

 tip and is almost absent anteriorly in Allothunnus, 

 as in Thunnus, 



Cleithrum 



The main body of the cleithrum in bonitos is 

 crescent-shaped with an anterodorsal spine and a 

 posteriorly projecting plate at the upper end, as in 

 other scombrids (Figures 61, 62). The angle 

 between the spine and the dorsal margin of the 

 plate is smallest in Gymnosarda and widest, al- 

 most a right angle, in the species of Sarda. The 

 angle is intermediate in Cybiosarda, Orcynopsis, 

 and Allothunnus, similar to the condition in 

 Thunnus. Godsil (1954) stated that the posteriorly 

 projecting plate in S. velox ( = S. orientalis) has a 

 bluntly rounded distal end compared to S. chilien- 

 sis, which has the plate tapered distally. We found 

 that this character is not consistent in S. orien- 

 talis, but S. chiliensis does have a more tapered 

 distal portion than do the other species of Sarda. 

 The main body of the cleithrum consists of an 

 inner and an outer shelf, which join at the main 

 axis, and a ridge at the anterior margin of the 

 main axis on its inner surface. Cybiosarda, Or- 

 cynxypsis, and Sarda have a poorly developed ridge 

 along the anterior margin of the outer shelf 

 (Figure 61a-d) as does Thunnus (de Sylva 1955, fig. 

 34). It is present only along the posterior edge of 

 the upper two-thirds of the inner shelf of Gym- 

 nosarda. In Allothunnus (Figure 64f), the ridge 

 becomes a broad well-developed inner shelf which 

 extends internally from the outer shelf and at 

 right angles to the inner shelf along the upper 

 two-thirds of the main body. Orcynopsis has an 

 expanded lower portion of the inner shelf; in 



Figure 61.— Left cleithra of six species of Sardini, external 

 view. a. Cybiosarda elegans, New South Wales, 355 mm FL. b. 

 Orcynopsis unicolor, Tunisia, 495 mm FL. c. Sarda australis, 

 New South Wales, 495 mm FL. d. Sarda chiliensis, La Jolla, 

 Calif., 453 mm FL. e. Gymnosarda unicolor, Truk Islands, 696 

 mm FL. f. Allothunnus fallai, Tasmania, 680 mm FL. 



ANTERIOR 

 SPINE 



POSTERIOR 

 PLATE 



INNER SHELF 



OUTER 

 SHELF 



585 



