VERTEBRAL NUMBERS IN SHARKS — SPRINGER AND GARRICK 79 



from Norway, reported a statistically significant difference between 

 males and females in numbers of monospondylous ("whole vertebrae") 

 and diplospondyloiis ("half vertebrae") centra and in total number of 

 segments (counting each whole vertebra or each two half vertebrae 

 as one segment). Females had the higher average in each of these 

 three categories but in none did the average difference exceed half a 

 unit. Using Punnett's figures (for adults and embryos) we have 

 plotted frequency distributions of total vertebrae (each whole or half 

 vertebra of Punnett equals one vertebra in our study) and averaged 

 them: 



Total vertebrae 81 82 83 84 85 86 87 88 89 90 91 Average 

 Males 4 14 41 51 63 39 19 9 3 2 - 84. 73 



Females 3 12 39 71 84 55 33 20 3 - 2 85.02 



A t test of these data gives the value 2.06, which is not significant 

 at the 95 percent level; however, a t test of the number of mono- 

 spondylous vertebrae of adults gives a value which is significant 

 above the 99.1 percent level. Punnett did not allow for possible 

 year-class differences and it is not possible to tell from his data if there 

 is bias. A study of sexual differences in vertebral counts based on 

 embryos of a single year class would offer a solution to this problem. 



If the nature of sexual dimorphism in vertebral counts of sharks 

 is generally of the magnitude shown by E. spinax, it is not surprising 

 that our counts, based on small numbers of specimens, do not indicate it. 



mr A 1 / length penultimate monospondylous centrum ,^^„\ ti 



The A values ( — -, — ^,, a . ,■ , rh — 1 X100)> like 



V length first diplospondylous centrum / 



the vertebral numbers, vary widely within families and genera 



but within the species are relatively constant. The A values are 



smallest in the Lamnidae, Alopiidae, Triakidae, Carcharhinidae, and 



Sphyrnidae. The A values, up to about 300, are greatest in the 



Carcharhinidae, a family with great variation in this proportion. 



Families containing some species with A values of about 200 include 



the Scapanohynchidae, Triakidae, Sphyrnidae, Squalidae and Dala- 



tiidae. 



rpi Tj 1 /^r, / length penultimate monospondy lous centrum .yir,n\ 

 JL ne jj values i -j-. r 7 tt'. — 7 t — ^ — — xioo 1 



\ diameter of penultimate monospondylous centrum / 



are in general as inconsistent within the families and genera as are the 

 A values. The range of the B values is from about 25 {Alopias spp.) 

 to 200 (Isistius hrasiliensis) . 



If a B value of 75 or less is arbitrarily considered low and one of 

 125 or more is considered high, 13 of the 18 large sharks (attaining 

 a size of over six feet) for which we have data are indicated as having 

 low B values. Small species may have either high or low B values, 

 but of the 30 species of sharks having high B values, only one, the 



