VERTEBRAL NUMBERS IN SHARKS — SPRINGER AND GARRICK 81 



Squalus acanlhias is considered a cii-cumglobally distributed species 

 in the temperate waters of both the northern and southern hemispheres 

 although it is reported infrequently from subtropical areas. Our 

 evidence (table 1) indicates that at least in the northern hemisphere 

 the Atlantic population (with 79-85 precaudal vertebrae in 7 speci- 

 mens) and the Pacific population (with 68-76 precaudal vertebrae in 

 21 specimens) have differentiated. Six specimens from the southern 

 hemisphere have 75-78 precaudal vertebrae and thus are intermediate 

 between the northern hemisphere populations. A large-scale study 

 of vertebral numbers in this species might yield interesting informa- 

 tion on speciation. 



On the basis of the counts obtained for Centrophorus uyato, there 

 is evidence that differences occur in the populations from the Gulf of 

 Mexico and the eastern Atlantic. More counts will be necessary to 

 verify this indication. 



The genus Etmopterus is d stinct from all other shark genera ex- 

 amined in consistently having the last monospondylous centrum at 

 a point behind the tip of the pelvic fin (pi. 1b), usually under the 

 anterior portion of the second dorsal fin. In all other sharks we have 

 investigated, except a few species of Carcharhinus (Garrick, in ms.), 

 the last monospondylous vertebra occurs over the pelvic fin, usually 

 over the pelvic base. 



Punnett (1904) reported the total vertebral counts of 163 free-living 

 females of Etmopterus spinax. Twenty-five were gravid and were 

 reported with the counts of theu* respective embryos (see our table 3). 

 Examination of Punnett's data shows that the average number of 

 vertebrae in a litter exceeds the maternal count in 10 of the 13 mothers 

 with 82-85 vertebrae but is less than the maternal count in the 12 

 mothers with 86-88 vertebrae. Differences in counts from a single 

 litter range from two to seven vertebrae. We have found a similar 

 variation in the range of vertebral counts in carcharhinid sharks in 

 the few cases in which we have mothers with embryos. 



Only late-stage embryos of Echinorhinus cookei and E. brucus were 

 radiographed; the radiographs show no evidence of calcification of 

 the centra. 



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