We thank the curators of the collections listed 

 above for allowing us to examine specimens in their 

 care and providing X-ray photographs. We also 

 thank the many individuals in the field programs 

 listed above who have helped us. 



METHODS 



Methods and definitions follow Cohen (1958). 

 We note in particular that the split posterior ray 

 of the dorsal and anal fins is counted as two rays 

 and that the vertebral count does not include the 

 urostyle or the hypural fan. The method of count- 

 ing gill rakers is shown in figure 1. Meristic 

 characters are given as the mode followed by the 

 range in parentheses. Where the range includes 

 data for more than one species, no mode is given. 

 Measurements are given as the mean followed by 

 the range in parentheses. 



FIOUEE 1.— Argentina striata, USNM 203001. First gill 

 arch from left side ; rakers on lower arm are counted as 

 six. Gill filaments are not shown. Drawn by Mildred H. 

 Carrington. 



GENUS ARGENTINA LINNAEUS 



For this genus, we divide the species into two 

 groups and discuss sympatry and its significance, 

 taxonomic significance of the swimbladder, and 

 present a key to the species of Argentina. 



SPECIES GROUPS 



The 12 species of Argentvna are divided into two 

 groups. 

 Species Group 1 



Four species are in this group. They are silus 

 and sphyraena from the North Atlantic and Med- 

 iterranean and .^ialis and aliceae from the eastern 

 Pacific. This group is distinguished by its larger 

 jaw, almost always greater than 21.5 percent of 

 head length (fig. 2), and usually more gill rakers 

 (7-21 on the lower arm of the first gill arch ; one 



species, A. sphyraena, has few gill rakers, 7-10, 

 but the other three species have 11-21 ; see table 1) . 

 The species in this group are allopatric (although 

 the gross geographical ranges of sphyra^ma and 

 silus overlap, they are ecologically separate, 

 mainly living and certainly spawning at different 

 depths), and are very distinct morphologically. 



Species Group 2 



Eight species are in this group. They are striata, 

 brucei, georgei, and stewarti, all from the western 

 Atlantic; euchus, from the western Indian Ocean; 

 and elongata, australiae, and kagoshimae from the 

 western Pacific. This group is distinguished by its 

 shorter jaw, almost always less than 20 percent of 

 head length, and generally fewer gill rakers (5-10, 

 but one species, A. elongata, has more gill rakers, 

 8-10 ; the other species have 5-8) . At least some of 

 the species in this group are sympatric. 



SYMPATRY AND ITS SIGNIFICANCE 



Cohen (1958) treated the forms (then three, a 

 fourth is described in this paper) constituting the 

 silus group as full species. However, the three 

 western Pacific forms of the striata group, 

 austraUae, elongata, and kagosMmae, were recog- 

 nized as subspecies because these disjunct popula- 

 tions (Australia, New Zealand, and Japan, respec- 

 tively) are very similar to each other, far more so 

 than are the species in the silm group (see key). 

 A. striata was recognized as a full species, but 

 could just as easily have been ranked as a sub- 

 species. A. euchus (Cohen, 1961) was given full 

 species rank because it was described from only 

 two specimens. 



Subsequent study of hundreds of specimens from 

 the western Atlantic has shown that what was 

 formerly considered to be a single species, A. 

 striata, clearly comprises four forms. These forms 

 are similar to each other and separated by few 

 characters. In fact, they are distinguished, one 

 from the other, by characters which both qualita- 

 tively and quantitatively resemble those that 

 separate the western Pacific forms. 



We recognize the four closely related western 

 Atlantic forms as full species because at least some 

 of them are sympatric. A striata and hrucei have 

 been taken together in trawl hauls off Venezuela 

 {Atlantis sta. 2700; Oregon sta. 1989, 4410, and 

 4465). A. hrucei and steivarti were taken together 

 off Nicaragua {Oregon sta. 3574 and 3610). A. 



14 



U.S. FISH AND WILDLIFE SERVICE 



