PROF. W. H. FLOWER ON THE GENUS MESOPLODON. 429 



bury Museum, New Zealand, which has C. 7, D. 10, L. 10, C. 19 = 46 (Haast,P. Z. S. 

 1876, p. 481). 



The cervical vertebra? of the two skeletons are very much alike ; indeed, considering 

 the difference of age and the great tendency to individual variation, it may be doubted 

 whether any differences that may justly be called specific can be detected between 

 them. In both the atlas and axis are completely united by the whole of the body and 

 arch, except for the spaces in the latter which constitute the foramina for the exit of 

 the second cervical nerves ; in both all the other vertebrse are perfectly free 1 . This is 

 the minimum of vertebral union known in any Ziphioid, and is the same which occurs 

 in the specimens of M. Helens at Brussels and at Gothenburg. In M. layardi the 

 atlas and the second and third cervical vertebra? are united into one large triangular 

 bone, the rest are all free 2 . In the skeleton of Berardius arnouxi, in the Museum of 

 the College of Surgeons, the third is united by its body to the completely conjoined 

 first and second. In the fine skeleton of Ziphius cavirostris from Villa Franca, in the 

 Museum at Jena, the first, second, and third vertebrse are completely united by their 

 bodies, and the fourth is joined to them by the spine. In another specimen from 

 Corsica, described by Fischer, the six anterior vertebras are united. In the Gothenburg 

 Ziphius the first four are joined. In Hyperoodon the bodies of all seven are firmly 

 united together, and the spines of all except the seventh join to form a single elevated 

 conical mass. 



The arch of the atlas bears in both specimens a complete foramen for the passage 

 of the cervical or suboccipital nerve, not a groove only, as in Berardius. In other 

 respects these bones bear a great resemblance to those of that genus, more than they 

 do to Ziphius and, a fortiori, to Hyperoodon. 



In M. grayi the upper and lower transverse processes of the axis are united on the 

 left side, leaving only a small circular foramen between them at the base ; but on the 

 right side in this specimen, and on both in M. australis, the processes are quite distinct, 

 and separated by a wide notch. In all the other vertebrae, as far as the sixth, the 

 upper and lower processes are present and not united. They are developed in a nearly 

 corresponding degree in the two specimens, except that in the sixth vertebra the upper 

 process is very rudimentary in M. australis, and the left lower process is developed to 

 nearly double the length of the right. This is evidently an individual peculiarity. 



These processes differ very considerably from the corresponding parts of Berardius, 

 as they are directed downwards, outwards, and in the main backwards, instead of for- 

 wards as in Berardius, in which it is the anterior portion of the process, and not the 

 principal or posterior part, which is chiefly developed 3 . 



The arches and spines of the cervical vertebrse are better developed generally than in 



1 Dr. Haast tells me in a letter (Dee. 12, 1876) that in the skeleton of an adult female of M. grayi the third 

 cervical vertehrais united to those before it. 



2 Haast, P. Z. S. 1876, p. 482. 3 See Trans. Zool. Soc. vol. viii. p. 225. 



