430 



PEOF. W. H. FLOWER ON THE GENUS MESOPLODON. 



Berardius. They are all completely united above, except the fifth of the young M. grayi. 

 In the sixth, in both specimens, the spine is so well developed as to equal in height the 

 spinal canal over which it is placed. In the seventh, in M. australis, it is considerably 

 higher than in M. grayi, and also much stouter at the base. It is a question, however, 

 how much the difference between the two may be due to age. The seventh in both 

 has a large articular surface on the posterior edge of the side of the body for arti- 

 culation with the head of the first rib. At the lower end of this surface is a small 

 tubercle representing the inferior transverse process of the preceding vertebra. 



Dimensions of the Cervical Vertehroe. 



Antero-posterior length of the bodies of the seven vertebrae in con- 

 tact (inferior surface) 



Length of body of united first and second 



Length of body of seventh 



Height from top of spiue to lovrcr edge of body of atlas 



„ „ „ third vertebra . . 



;, „ „ sixth vertebra . . 



„ „ „ seventh vertebra. 



Breadth between outer borders of articular surfaces of atlas 



Breadth between ends of transverse processes of atlas 



It will be seen from the above that the only measurement in which M. grayi exceeds 

 M. australis is the width of the surfaces for articulation with the occipital condyles. 

 This, taken in conjunction with the immaturity of the specimen, is a tolerably sure 

 indication that it would, if adult, attain a larger size than the latter. 



The thoracic vertebrae of both skeletons present all the characteristic features of the 

 group, the most remarkable of which is the sudden transition of the articulation of the 

 ribs fi-om the upper to the lower processes, by which the Physeteridse are distinguished 

 from the Delphinidse. The principal difference between the two is that in M. australis 

 there are but nine with nine pairs of ribs (as in Tlyperoodon), whereas in M. grayi there 

 are ten, as in all the other recorded examples of Mesoplodon \ 



In the erect high spines of the thoracic vertebrae Mesoplodon resembles both Ziphius 

 and Hyperoodon, and differs in a marked manner from Berardius ^. 



' It should be mentioned that, according to Hector's original description (Trans. N.Z. Inst. vol. vii. p. 262), 

 the skeleton of M. australis had ten pairs of ribs; but the number now present with it is that which I have 

 stated above, and the vertebra which I have reckoned as the first lumbar bears no trace of an articulation for 

 a rib at the end of the transverse processes. Moreover a close comparison shows that the rib which is wanting 

 would not correspond to the last of M. graiji or the other ten-ribbed species, but rather to one from the middle 

 of the series ; and yet there is no indication of the accidental loss of both vertebra and pair of ribs, which must 

 have been the case if Dr. Hector's enumeration was correct. 



' See Trans. Zool. Soc. vol. viii. p. 226. 



