SPEARFISHES OF THE CENTRAL PACIFIC 



517 



25 30 35 



CAUDAL SPREAD AS PERCENT OF FORK LENGTH 

 Figure 21. — Mean, standard deviation, and range of the ratio of caudal spread to fork length. 



40 



in rigor. On the other hand, the pectoral fins of 

 marhns in rigor move stiffly at all times, but we 

 have not yet encountered an ampla or audax, 

 even though in rigor mortis, whose pectoral fin 

 could not be folded back against the body without 

 breaking. 

 Miscellaneous characters 



We have not used a number of other characters 

 because they are too variable, too similar among 

 species, or our data too few. The depth of the 

 head in marlina appears to be greater than in the 

 other species, but when measured from the supra- 

 occipital to the isthmus we found this character 

 to be highly variable. Perhaps this is because it 

 is so difficult to standardize the position of the 

 branchiostegal rays after death. Also, the bod^' 

 of both marlina and audax appears to be definitely 

 more tapered than that of ampla. We attempted 

 to measure this by obtaining a depth at the vent 

 to compare with the greatest body depth but had 

 too few measurements to establish any relation. 

 Then the sword in marlina appears definitely 

 heavier and more robust than that of the other 

 two species; but when the breadth is measured at 

 the tip of the mandible we find a great deal of 

 overlap, probably because, as pointed out earlier, 

 the mandible becomes shorter in relation to ttie 

 sword in ampla, whereas in audax and niarlina it 

 grows nearly isometrically. (It would be better 



to measure the width and depth of the mandible 

 at the midpoint.) On another occasion, when we 

 had an opportunity to examine a specimen of 

 marlina alongside an ampla of about the same 

 weight, we noticed that the distance between the 

 ventral groove and the insertion of the anal fin 

 in marlina was considerably greater than in ampla. 

 However, a few more measurements of this char- 

 acter suggest that it also is extremely variable. 



The principal criteria used by Jordan and Ever- 

 mann (1926) to separate the nominal species 

 properly referable to the genus Tetrapturus are the 

 presence or absence of short, stiff spines between 

 the two dorsal fins or between the two anal fins 

 and the width of the interspaces. We doubt 

 the value of these characters in distinguishing 

 the species, because in the few shortnose spearfishes 

 examined we found the interspace between the two 

 dorsals to be highly variable and in one specimen 

 even lacking. We have found no free spines in our 

 specimens of Tetrapturus, but liave noticed them 

 occasionally in ampla, and have even found them 

 in separate fin slots. In most spearfishes the 

 posterior spines of the first dorsal fin become very 

 small, and whether they an> separate is not easily 

 determined uidess they happen to be in separate 

 fin slots. We consider the interspace between the 

 aiials and dorsals and tlie number of free spines to 

 be of very doubtful value as taxonomic characters. 



