SILURIAN RIVAL VED MOLLUSCA OF VICTORIA. 
The large majority of the species of Silurian bivalves herein 
described are in more or less close relationship with those found 
elsewhere; at the same time they appear to be sufficiently dis- 
tinct to warrant their separation as new species. When closely 
examined, the data afforded by these “ paramorphs " or allied 
forms, are of the greatest interest; for these, as well as the more 
cosmopolitan species above enumerated, shed considerable light 
upon the generally obscure questions regarding the relationship 
of our Australian palaeozoic faunas to those of other areas. 
The subjoined table is an attempt at giving a synopsis of 
the species described from other areas, which, apparently, are 
most closely related to the Victorian Silurian pelecypoda. A 
glance at this table will suffice to show that, as in the former 
table of identical species, the general aspect is nearly the same 
with regard to the several areas known elsewhere. 
In Great Britain and Ireland some of our species find their 
affinities with Upper Ordovician forms (very rarely), with 
Silurian, Llandovery to Ludlow (commonly), and in the 
Devonian (very rarely). In Germany related species occur in 
the Devonian (very rarely). 
In Bohemia their relationships are found in typical 
Silurian and Lower Devonian strata (rarely). 
In Canada, a single allied form occurs in the Silurian. 
In the United States the many related forms range through 
the Devonian, from the Hamilton to the Waverley groups; 
whilst only one species having related characters is found in the 
Upper Ordovician. 
The question as to whether the Lower Helderberg group in 
North America should be correlated with the Devonian, as main- 
tained by Continental geologists, who recognise in it the equiva- 
lent of the Coblenzian; or with the Silurian, as held by American 
geologists, is a difficult point to determine. The fauna of the 
uppermost beds of the Silurian in Victoria seems to support the 
American geologists to some extent; for it includes many types 
of trilobites, many representatives of the Cct/pulidce, and 
certain spirifers which, although characteristic of the Hereynian 
fauna of Europe, are also Helderbergian in aspect. There seems, 
therefore, as much evidence in support of the one opinion as the 
other, and it is merely a question of recognising the possibility 
of the subsequent migration to another area of a distinctive 
fauna, with a minimum amount of change in its facies. 
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