The sex of each animal was thoroughly ascertained; and in connection with the
two sexes I have to point out that, although the males, 6, 7, and 8, from the Hughli,
are fully adult, they are very much smaller in every way than adult females from
the same stream. The skeleton of the male No. 6 is 18*50 inches shorter than that
of the female No. 1. The great difference that exists between the size of their skulls
is well established by Plate XXXIX, in which fig. 1 is a representation of the male
skull and fig. 2 is that of the female skull, the two having been photographed together.
The skull of the female is 27*25 to 19*40 inches in the male, that is 7*85
inches longer. I t will also be observed that the osseous snout of this female is proportionally
longer than the rostrum of the male, but both are about the same, depth
at the middle, the depth of the conjoint jaws between the eighteenth and nineteeth
teeth is in the male 3*20 to 3*25 inches in the female at the same point. The
curvature of the snout is much the same in both, there being a considerable upturning
of the extremity of the maxillaries and of the mandible. The trifling differences
observable between the form of the maxillary crests of figs. 1 and 2 (Nos. 6 and 1 of
tables) are of no importance, as these structures are variable; and the outline of the
frontoparietal suture also differs considerably in different individuals of the same
sex, and even on opposite sides of the same skull. In all their essential features,
therefore, the male skulls, although much smaller, correspond to the female skulls,
but their teeth, although proportionally smaller than in the females, preserve the
same characters, their bases being much extended from before backwards and worn
flat. The male dolphins which I have tabulated, beyond being smaller and having
shorter snouts, show no other external features in which they differ from the females.
The question, however, suggests itself, axe these differences to be regarded as specific
or merely as sexual ? I am disposed to adopt the latter alternative, but at the same
time, as still larger individuals are met with in the Granges than any I have yet
mentioned, and mature females occur smaller than No. 1 of the accompanying
tables, my opinion on this point is not fully established. The skeletons Nos. 3 and
4 of these tables appear to be younger stages of the same specific form as No. 1,
with long slender jaws and the sharply pointed teeth of adolescence, but a difficulty
presents itself regarding the dolphin kindly forwarded to me by Mr. Olay, C.S., who
took great interest in this enquiry. (See Table I ? 1).
This specimen was harpooned on the 23rd June 1867, near Meerpore on the Suraj
fork of the Bansi branch of the Ganges, about 10 miles north-west of Dacca, and
Mr. Clay forwarded to me a sketch of the animal in the flesh with the measurements
given in the accompanying table, along with the skeleton of the animal. Mr. Clay’s
drawing corresponds essentially to my Plate XXY, figure 1 of -P. gangetica, but the
teeth that remained in the jaw are represented as very large and much worn, indicating
that the dolphin was, considerably aged—a fact verified by the condition of the
skull and skeleton. By the time the skeleton reached me all the teeth had fallen out
of their sockets, the latter being well filled up with osseous deposit. The jaws,
although having much the same form and relative length to the rest of the skull as
in the female skull, Plate XXXIX, fig. 2, are much more feeble and have less depth,
the entire animal being 10 inches shorter thafc the largest female from the Hughli,
in which the condition of the teeth was that of a fully mature, but not aged
animal. Another female from the Hughli with its teeth indicating adolescence, and
having a long, attenuated, and not deep snout, has its skull only a quarter of an inch
shorter than thé skull of Mr. Clay’s dolphin, and its adolescence is so pronounced
that we may justly concludé that the animal would have attained to the dimensions of
the largest recorded female from the same river. But the condition of the skull and
skeleton of Mr. Clay’s specimen leads to thé conclusion that its period of growth was
passed. Mr. Clay’s specimen, it will be observed, was from the neighbourhood of Dacca,
and as the differences that exist between it and thé adult from the Hughli lie chiefly
in size, it may be that theré is à smaller race, for the skulls are so alike in all their
essential features that the Dacca skull cannot be regarded as of a specific type.
Moreover, I have had the opportunity to compare, side by side, in the flesh, two
dolphins, one of the male and the other of the female sex, the former from the
Hughli and the latter from Dacca, and after a most careful observation of these; in
view of this question of the probability of the existencex of more than one species
of Platàmsta in the Gangetic and Brahmaputra systems, I have failed to detect any
character by which they could be separated. However, if we take the condition of
the alveolar sockets of Mr. Clay’s specimen, as indicating that the animal was aged,
which I believe we axe entitled to do, then it follows that it is as old, if not older,
than a skull of another specimen from the Ganges opposite to Chupra, in the Saran
district, and which was caught in May 1870 and for which I am indebted io
Mr. Garret, C.S. But this skull is 7 inches longer than the skull from Dacca, and is
thus of great size. The few teeth that remain in the jaw are all flattened, and some
of them are 0*68 inch in breadth. All the bottom of the alveolar groove is filled
up as in Mr. Clay’s dolphin, but the sockets are not so obliterated. With these facts
in view it seems highly improbable that the latter could ever have attained to the
dimensions of the large Chupra skull, which, in its features, Jias such a close resemblance
to the largest females from the Hughli, that I am disposed to consider it of
the same sex. Not having seen the Chupra specimen in the flesh, I can say
nothing regarding its external characters. In its rostrum, however, it differs somewhat
from large females from the Hughli in that the end of the snout, instead
of being upwardly dirécted, is downwardly bent ; but- this character is probably
the effect of age, as it occurs in other dolphins, and has been noticed by Professor
Elower in Inia and Pontoporia, the former being nearly allied to Platcmista. The
lower jaws of both axe alike. Some of the males from the Hughli conform more
to the Chupra skiill than to the skull of Mr. Clay’s specimen, but that they could
never have attained to the same size is conclusively proved by the complete ossification
of their epiphyses.
The large skull of Mr. Garret’s specimen measures 30 inches in extreme length,
and is thus about 2*75 inches longer than the largest female skull from the Hughli,
and 10*60 inches longer than the largest male skull from the same river, the male skull
(No. 6) being fully adult, the teeth being very broad at their bases, but still more or