22%
WILLIAM MACNAE
and relevant t o the present discussion is the distribution of two species,
Hydrophis torquatus and H . fasciatus, each with two or more subspecies.
Of these H . t. torquatus and H . f . fasciatus are distributed from India t o
the northern approaches to the Straits of Malacca. H . t. aagaardi
extends from eastern Malaya t o Borneo, the Philippines and South
China, while H . f . atriceps extends from eastern Malaya to Borneo,
South China and Australia.
Mayr (1944), de Beaufort (1951), Tweedie (1954) and Hall (1962)
have all noted the importance of the subcontinent of Sundaland which
was in existence during much of the Pliocene and throughout the
Pleistocene (Fig. 75).
Mayr was concerned chiefly with the terrestrial fauna and Wallace’s
line. He showed that this line, marking as it does the edge of the Sunda
Shelf (i.e. the old shore line of Sundaland a t its greatest extent),
indicates the farthest that a purely terrestrial fauna could extend
over the Indo-Australian archipelago. Similarly the edge of the Sahul
Shelf marks the limits reached by the continental Australian fauna.
The islands between have been invaded from both sides and show a
mixture of impoverished Asian and Australian faunas. De Beaufort is
in agreement with this, and van Bentham Jutting in a series of papers
on the freshwater and estuarine molluscs also indicates the importance
of these continental shelves.
Tweedie and Hall are concerned only with marine crustaceans. Both
hold that the existence of Sundaland for such a long time separated the
Indian Ocean fauna from that of the South China Sea and permitted the
development of sibling varieties and subspecies and even of species. It
is only within historic times that these faunas have been brought into
contact by the opening of the Straits of Malacca. Both these authors
show that differences exist between the faunas of the west and east
coasts of Malaya and they argue that mixing is, though not prevented,
certainly hindered by the set of currents and by tidal turbulence at the
southern entrance to the Straits.
Table I1 gives Tweedie’s list of crabs so making this distinction
clear. Hall recognized similar distinctions and differences between
penaeid prawns. Crane (in Zitt.) also suggests that this land mass has
been important in relation to speciation and distribution of fiddler
crabs (Uca spp.). Guinot and Crosnier (1964) have shown too that of
two sibling species of Sesarma, S. longipes extends from Natal to the
Andamans while S. kraussi replaces it in the Straits of Malacca and a
subspecies X. k. borneensis continues the range eastwards.
It would appear that S. kraussi is a species which probably within
historic times has spread by the prevailing northwards-tending tidal
WILLIAM MACNAE
and relevant t o the present discussion is the distribution of two species,
Hydrophis torquatus and H . fasciatus, each with two or more subspecies.
Of these H . t. torquatus and H . f . fasciatus are distributed from India t o
the northern approaches to the Straits of Malacca. H . t. aagaardi
extends from eastern Malaya t o Borneo, the Philippines and South
China, while H . f . atriceps extends from eastern Malaya to Borneo,
South China and Australia.
Mayr (1944), de Beaufort (1951), Tweedie (1954) and Hall (1962)
have all noted the importance of the subcontinent of Sundaland which
was in existence during much of the Pliocene and throughout the
Pleistocene (Fig. 75).
Mayr was concerned chiefly with the terrestrial fauna and Wallace’s
line. He showed that this line, marking as it does the edge of the Sunda
Shelf (i.e. the old shore line of Sundaland a t its greatest extent),
indicates the farthest that a purely terrestrial fauna could extend
over the Indo-Australian archipelago. Similarly the edge of the Sahul
Shelf marks the limits reached by the continental Australian fauna.
The islands between have been invaded from both sides and show a
mixture of impoverished Asian and Australian faunas. De Beaufort is
in agreement with this, and van Bentham Jutting in a series of papers
on the freshwater and estuarine molluscs also indicates the importance
of these continental shelves.
Tweedie and Hall are concerned only with marine crustaceans. Both
hold that the existence of Sundaland for such a long time separated the
Indian Ocean fauna from that of the South China Sea and permitted the
development of sibling varieties and subspecies and even of species. It
is only within historic times that these faunas have been brought into
contact by the opening of the Straits of Malacca. Both these authors
show that differences exist between the faunas of the west and east
coasts of Malaya and they argue that mixing is, though not prevented,
certainly hindered by the set of currents and by tidal turbulence at the
southern entrance to the Straits.
Table I1 gives Tweedie’s list of crabs so making this distinction
clear. Hall recognized similar distinctions and differences between
penaeid prawns. Crane (in Zitt.) also suggests that this land mass has
been important in relation to speciation and distribution of fiddler
crabs (Uca spp.). Guinot and Crosnier (1964) have shown too that of
two sibling species of Sesarma, S. longipes extends from Natal to the
Andamans while S. kraussi replaces it in the Straits of Malacca and a
subspecies X. k. borneensis continues the range eastwards.
It would appear that S. kraussi is a species which probably within
historic times has spread by the prevailing northwards-tending tidal