104 STUDIES OF TASMANIAN CETACEA, 



Tursioys furnishes a most useful text for an osteo- 

 logical study, as the genus' — in point of size^ — is midway 

 between the Orcas upon the iipgrade, and. the porpoises 

 upon the down grade. The common Dolphin, which 

 ranges in our seas up to eight feet in length, presents 

 osteological characters worthy of a separate study, and, 

 therefore, in this paper it is proposed to present a com- 

 parative study of the male and female Tursiops, rather 

 than to contrast with Globicephalus or Delphinus, as would 

 most commonly obtain. 



MALE SKULL. 



The occipital condyles are very heavy in appearance, 

 and divergent upon their upper margins, so that the space 

 between them and the magnum foramen — with which their 

 upper ends terminate — is eixa,ctly two inches, while three- 

 "•uarters of an inch below the foramen they have so con- 

 tracted that the intervening space is only three-eighths of 

 an inch. From this point, however, they again diverge 

 in a rounded curve to their bases — a fourth of an, inch 

 lower down. The magnum foramen is buried away under 

 the overlaiDping condyles, which latter form two hollow 

 grooves along its margins, terminating above in two deeply 

 marked pits. The foramen itself measures 1| x 1| 

 inches, and is arched, rather than notched, upon its upper 

 border in the individual skull here used for descriptive 

 purposes. Some male skulls, however, available to us, 

 show the notch most distinctly, while female skulls, ap- 

 parently, have the magnum foiamen transversely oval, 

 and quite devoid of either notch or distinct arch. When 

 large numbers of these skulls, of various ages, and both 

 rsexes, are available for direct comparison, it will most 

 probably be shown that the following facts obtain : — 



1. All young Tursiops' skulls have a transversely oval 



magnum foramen. 



2. The majority — if not all — females retain this form 



throughout life. 



3. Adolescent males show the inception of the up- 



ward enlargement of the foramen, in the im- 

 mediate centre of the upper wall, and thus con- 

 stitute "a notch." 

 t 



4. Later in life, the edges of the notch become ab- 



sorbed, as the needs of the medulla oblongata 

 demand, and the "arched" upper edge of the 

 foramen is the result. 



