THE SOUTHERN BOTTLENOSED WHALE 31 



this process is almost complete, with capitulum and tubercle of the seventh rib having articulation 

 almost completely restricted to the seventh thoracic vertebra. 



The change in position of the transverse process from the side of the neural arch (upper transverse 

 process of Flower, Osteology, 1870, p. 60) to the side of the centrum (lower transverse process of 

 Flower, op. cit.) takes place in the eighth vertebra. There is not in the Discovery specimen as in the 

 South Australian specimen a vertebra showing the transition from the one to the other kind of 

 transverse process. The H. rostratus specimen used for comparison with H. planifrons showed in the 

 eighth vertebra a condition intermediate between that of the other two specimens. In it the upper 

 transverse process is in the form of a small knob-like and quite vestigial process on the lower margin 

 of the metapophysis. 



Going tailwards the ventral surface of the centrum shows increasing development of the median 

 ridge which is in the form of a well-defined keel on th. VIII. 



Lumbar vertebrae. There are eleven vertebrae in the lumbar series of the Discovery H. planifrons. 

 The South Australian specimen has one less, but this discrepancy may be accounted for by the 

 greater number of thoracic vertebrae in the latter specimen. 



The neural spines increase in length to about the middle of the series and then diminish gradually, 

 so that a line joining their extremities makes a very shallow arcr There is an increasing inclination 

 backwards of the spines going tailwards, a widening of the spine as a whole and of the distal end as 

 well in the more posteriorly situated elements. The metapophyses are laminar, have rounded margins, 

 and show increasing approximation to each other. The neural canal diminishes in size ; the centrum 

 increases so that at the end of the series it is about i J times the length of the first lumbar ; the diameter 

 also is increased. The transverse processes are directed obliquely forward, flattened, beginning to 

 diminish in length, and get wider at the tail end of the series. The first lumbar transverse process is 

 somewhat different from those that succeed it, being disproportionately broad and rather stouter. 



The hypophysial ridge is of increasing definition to about the middle of the series, whence it 

 diminishes in prominence ; and in the last lumbar it is a low, flattened, inconspicuous keel. 



No obvious differences distinguish the vertebrae in this region from those of H. rostratus. 



Caudal vertebrae. The caudal series of vertebrae is incomplete in the Discovery specimen. Seventeen 

 remain and the missing elements are at the posterior end. The South Australian specimen has 

 20 caudals. 



The neural spines diminish tailwards and disappear after the tenth caudal. In lateral view they 

 are broad distally with a slight narrowing towards the neural canal. There is a corresponding diminution 

 of metapophyses which anteriorly in the series are laminar with rounded border, and posteriorly are 

 rather stout short tubercles which finally disappear. The neural canal continues the diminution in 

 size observed in the lumbar series. 



Anteriorly the centra have the massiveness which characterizes the more posteriorly placed lumbars 

 and, going tailwards, although length diminishes gradually, the decrease in transverse diameter is 

 not noticeable until near the end of the column where the diminution becomes more marked and the 

 vertebrae adopt a subcuboid shape unlike the cylindrical form of the more anterior elements. 



The transverse processes disappear as distinct prominences after the seventh caudal. While still 

 distinguishable they maintain the obliquely forward direction noted in the lumbar vertebrae. The 

 perforation of the transverse process of the seventh, noted by Dale, is represented in the Discovery 

 specimen by a pronounced emargination of the outer edge of the process on each side near its posterior 

 end. This is visible, although much less obvious, on the transverse processes of two vertebrae im- 

 mediately anterior to the seventh caudal. 



On the lower surface of the centrum anteriorly and posteriorly are the paired facets for the chevron 



