1893.] CETACEAN GENUS MESOPLODON. 219 



N. A cranium of an immature example of M. layardi in the 

 "Wellington Museum, N. Z. ; sex unknown. 



O. A cranium of a young individual of M. layardi, in the Napier 

 Athenseum, N. Z., in which the vomerine trough is quite empty 

 and smooth ; sex unknown. 



P. A cranium of an aged individual in the British Museum, 

 evidently a male. 



Q,. For purposes of comparisou with the species of Mesoplodon, 

 I have exnmined the skeletons of Zipliius cavlrostris {^Epiodon 

 chathamensis) in the Canterbury Museum, N. Z. 



B. A cranium of a very young individual of Ziphius cavlrostris, 

 collected by myself in the Chatham Islands in January last (1892), 

 and now iii the Canterbury Museum, in which the vomerine spout 

 is quite empty and smooth, except on the bottom of the trough, 

 where there is a small upgrowth. 



8. A aVehton oi ZijJtlKS {Eplodon) chathamensis { = Z^ cavlrostris) 

 in the British Museum collection. 



T. A cranium of Ziphius cavirostHs (the type) in the British 

 Museum. 



XT. A younger cranium than T, of Ziphius cavirostris, in the same 

 collection. 



V. A skeleton and two crania of Berardius arnuxii, in the 

 Canterbury Museum, N. Z. 



With these I have also compared the various fossil species in 

 the Geological Department of the British Museum, Mesoplodon 

 ungustus, M. gihhus, Choneziphius pdanirostris, and G. planus. 



Por the opportunity of examining one or more of the above 

 enumerated specimens I am greatly indebted to the kindness of 

 Dr. Giinther, F.K.S., and Dr. Woodward, F.K.S., of the British 

 Museum ; to Professor Stewart, P.L.S., Eoyal College of Surgeons, 

 Prof. T. J. Parker, P.E.S., Dunedin, N. Z., Sir James Hector, 

 r.E.S., Wellington, N. Z., and to the authorities of the Hawke's 

 Bay Philosophical Society in Napier, N. Z. 



Prom an examination of these specimens I have come to the 

 conclusi(m that the species of Mesoplodoii, and certainly some of 

 Ziphius, change very greatly in regard to the form of their rostra 

 with age and sex ; and from the transverse sections of various rostra 

 that I exhibit it will be apparent that the contour of each varies 

 with the amount of ossification and consolidation of the rostral 

 bones in different sexes at different ages. It will then be seen, I 

 think, that the species designated Mesoplodon hectori, Gray, by 

 Hector and Haast, and Mesoplodon australis and Mesoplodo7i haasti 

 by Sir W. Plovver, are really more or less aged forms of Mesoplodon 

 g'rayi, Haast. In his paper in the ' Transactions ' of the Zoolo- 

 gical Society already referred to. Sir W. Plower has been careful 

 to remark : — " Under the circumstances it is somewhat difficult to 

 know what course to pursue with reference to the names by which 

 these specimens are to be respectively distinguished ; but on the 

 whole it will lead to less confusion if I designate them, provi- 

 sionally at least, by specific appellations, bearing in mind that it 



