80 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lie 



unique Scapanorhynchus owstoni, attains a size greater than six feet. 

 These facts seem to indicate that B values are functionally significant 

 in terms of total length attained by the species. 



Remarks Concerning Certain Species 



In Hexanchus and Notorhynchus the vertebrae are not sufficiently 

 calcified to produce an image on a radiogi'aph. In Heptranchias , the 

 precaudal vertebrae are poorly calcified and there is considerable 

 spacing between the images on the radiograph, which probably 

 indicates that only the center or the ends of each centrum are registered. 

 The caudal vertebrae are well calcified but terminate abruptly at about 

 the level of the subterminal caudal notch in each specimen, a condition 

 not noted in any other species we examined. 



In Chlamydoselachus anguineus only some of the vertebrae are 

 calcified; hence, total counts could not be made. In one specimen the 

 anterior 16 and posterior 3 precaudal centra and a few anterior caudal 

 centra were apparent; in the other specimen radiographed, the anterior 

 18 and posterior 9 precaudal centra and the anterior 20 caudal centra 

 were apparent Goodey (1910) indicated the number of vertebrae in a 

 specimen he dissected to be 112, on the basis of the number of neuro- 

 meres, which were determined by counting the ventral-root foramina 

 of the spinal nerves perforating the basidorsals. We believe that 

 counting in this manner yields a figure which is much too low, for it 

 does not take into account the diplospondylous condition. It is also 

 obvious from Goodey's plates that no nerve roots issue from large 

 segments of the vertebral column. 



Aasen (1961) reported vertebral counts of 60 specimens of Lamna 



nasus from the western North Atlantic, as follows: 



Total vertebrae 150 151 152 153 154 155 156 157 158 159 160 161 

 Specimens 115698978141 



He noted that the number of precaudal vertebrae ranged from 83 to 89. 



One specimen of Paragaleus gruveli (USNM 196158) examined 

 (pi. 1a) had two separated groups of elongated (monospondylous) 

 centra in the precaudal region. If each of these elongated centra 

 were counted as two, the number of precaudal centra would be 77 and 

 the total count 147, which would be more in accord with the other 

 specimen examined from the same locality. 



Specimens of Sphyrna tihuro from Florida have much lower vertebral 

 counts than specimens from other localities. Counts from large num- 

 bers of specimens throughout the Atlantic and Pacific range of this 

 species should be made to determine the significance of the counts 

 shown by the Florida specimens. 



