it is all but complete. In O. flu/mmalis the tendency to division also exists in the
adolescent skull, hut to a much less extent, while in the adult there is little or no
indication of it. The measurements of these parts may be stated as follows:—- .
- , ¿Q. brevirostr ¡ O.flu inalis-
I#'24 1-32 1-24 1-80 1-88
Sutures of p a l a t i n e s ........................................- 0’16 0T6 0.00 0-52 0-60
Length of palatines obliquély across the palate . . . . .
The distance between the bases of the pterygoids where the palatines
intervene is greater in 0 . Jluminalis than in the other species,
and may he tabulated thus, v is. . . . . . 0-52 0-52 0-64 0-64
The form of the palatines differs somewhat in the two skulls. They are
relatively larger in O. flwnmalis, and their middle margins are first directed backwards
and inwards and then markedly outwards and backwards, whilst in 0.
brevirostris the whole direction from their bases is outwards and backwards.
I lay considerable stress on the relations and form of the palatines, because
the characters I have described are persistent in Orcella brevirostris and in two
examples of O. Jluminalis, and, moreover, on referring to the skulls of two
species of an allied genus, Globicephalus, viz., G. svineval, Lacdp., and G. mdicus,
Blyth, I find they also are distinguished from each other by well-marked and
persistent characters in the form of their palatines. In G. indicus the pterygoids
are only separated from each other by a very narrow plate of the palatines, while in
G. svineval these bones are very broad and form a large surface widely separating
the pterygoids. I t is also a significant fact that one of the distinguishing features
of G. mdicus (G. macrorhynchus) from G. svineval is the relatively longer and
narrower snout of the latter as compared with the former—a condition the exact
reproduction of that which occurs in these small round-headed dolphins, in which the
proportionally shorter snout of O. Jluminalis has large palatines, while the longer-
beaked skull of O. brevirostris has these bones feebly developed.
Another distinction may be noted, viz., the more marked concavity of the supraorbital
plate of the maxillary of O. jkmi/nalis as contrasted with O. brevirostris.
. The tympanic and periotic are markedly distinct in the two species. In O.
jluminalis, the latter (Plate XLIII, fig. 4), when viewed from above, is seen to have
a different form from O. brevirostris (fig. 9) in the external half of its internal border,
which is prolonged backwards and outwards to the mastoid process in a swollen
outline, while the same part in O. brevirostris is concave. Anterior and internal
to this border the periotic is pyramidal in O. Jluminalis, awhile in 0. brevirostris
it is rounded and broad at its tip, and somewhat contracted at its base, and
of much greater size. The tympanic of O. jluminalis is proportionally larger than
in O. brevirostris, and slightly more pointed, and the' posterior inferior border
is flattened, instead of being rounded as in the latter. In O. brevirostris the posterior
lobe of the tympanic is not so long as in the Irawady dolphin, in which it is
not marked by the deep depression which occurs on the posterior surface of this part
of the bone of the marine form.
ORCELLA.
The dimensions of these bones are;—
O.fluminalii. P jB i
^Length of periotic . . . ■ • • ■ •
„ „ tympanic through anterior lobe . • . • • ■ • ■ •
- „ „ „ . f, posterior ,, . • • •' ’ • 1 • ' B • 1 1 •
Breadth o f tympanic at middle . . . • • • , • • • • •
Greatest breadtn . . . ,. . • . ■ - • _ • • » • • ’
1-64
T64
, 1-60
Ó-80
0-88
1-66
166
1-44
0-88
1-00
Table o f measurements o f the skulls o f Orcella brevirostris and Orcella Jluminalis.
Extreme length of skull in a straight line • • •
Greatest breadth across squamosals •
Length of snout from transverse line on preorbital notch
Breadth of snout at preorbital notch • ' . ‘
„ midway between preorbital notch and tip of snout .
„ between same points, following curve . . . .
Width of snout immediately behind its tip . • •_ _ ■
Breadth of occipitals between parietal sutures measured with calipers
Greatest hreadth across condyloid articular processes
Distance between condyles at.lower margin of foramen magnum .
>» „ occipital condyles at upper ditto .
Greatest breadth of each occipital condyle .
' length of same along curve • •
Length of foramen magnum . . • • •
Breadth of „ „' f • •
Width between lateral expansions of hasisphenoid . . . .
Greatest length of pterygoids on palatal surface .
„ of palatines in middle line o f palate
jj . width o f narial aperture • • •
Dentition.—The visible teeth are 1; Il I: it but in the upper maxillary, after
the flesh was removed, two on the right, and three additional sockets on the left
side, were displayed. The anterior teeth are much larger than those behind them,
and each is separated from its fellow by a very thin rough septum. In the left
division of the lower jaw the sockets are larger and deeper than in the upper jaw,
and on the right side fourteen sockets are well marked. Moreover, in the rough
surface that succeeds the last tooth upon each side of the lower jaw, there are indications
of what may have been the sockets of two other teeth. The first tooth in
the upper jaw is fully 0"-28 from the extremity of the premaxillaries, which are partially
worn, as if they had been undergoing decay. In the adolescent skull these
bones are almost intact at their tips. Erom the circumstance that the adult skull of
O. brevirostris in the fresh state only contained eight teeth in the upper jaw,
whilst when the jaws were freed of flesh they displayed a number of empty sockets
on both sides, it is evident that that form, and in all probability its near ally, O. flu-
minalis, lose their teeth with age from behind forwards ; likewise, that in the fully
matured condition they only retain eight or nine of the anterior teeth on each side
above and below. Decay seems to begin in the centre of the tooth, which is gradually
destroyed, leaving only the hard shell, which continues to project for some