FOSSIL FINBACK OF GAY HEAD. 287 



ners. The posterior cpiphysis is lost. There is no ventral pit to be seen, but the upper groove 

 is similar to that in the vertebra just described. The bone measures: 



Vertical diameter 76 mm. 



Transverse diameter 88 " 



Greatest fore-and-aft thickness 48 " 



Transverse width of dorsal groove 68 " 



The Museum of Comparative Zoology contains also a fragment of a cetacean rib which 

 I would refer with little hesitation to the genus Balaenoptera, and to the same species repre- 

 sented by the terminal bones of the spinal column. This fragment (no. 8744; Plate 15, fig. 9) 

 is from near the upper part of the rib, where it curves to articulate with the transverse process 

 of the vertebra. It is about 210 mm. long, and 80 mm. in diameter across its broader end. 

 It is much flattened and has on one surface a broad shallow groove running along its length 

 as in the living Balaenoptera. In the modern Right and Sperm Whales, the ribs are much 

 more rounded and stouter, without this groove. In section, the fragment is triangular at the 

 proximal end where the head of the rib begins to take shape; at the other end it is more nearly 

 oval in section, 35 mm. in diameter transversely. Judging from the shape of the fragment, 

 it must have come from one of the ribs near the hinder end of the series. 



Acknowledgments are due to the Museum of Comparative Zoology for the privilege of 

 studying and recording these as well as other specimens of New England Cetacea in its 

 collection. 



