SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
Actinodesma, Sandberger.—Although the hitherto-recorded 
range of this genus is restricted to the Devonian, there is very 
little doubt that it is represented in the Silurian (Upper Lud- 
low) of Wales by the so-called “ Avicula” or “Pterinea” 
ampliata, to which our fossil bears a close resemblance. 
Lunulicardium, Miinster.—This genus is confined to the 
Silurian and Devonian. In Bohemia it is found throughout 
both formations; in North America only in the Devonian. 
Mytilarca, J. Hall—Well-represented in the Devonian of 
North America. Jt occurs in the Silurian (Wenlock shale) in 
England, usually referred to as Mytilus. The British Silurian 
fossil recorded as Mytilus chemungensis seems to difier 
from the species originally described by Conrad from the 
North American Devonian. The genus occurs in the upper 
division (Yeringian) of the Victorian Silurian. 
Glossites, J. Hall.—Fossils of Devonian age in North 
America (Corniferous Limestone to Waverly Group); and in 
South Africa (Bokkeveld Beds). 
Cypricardinia, J. Hall—This interesting genus ranges 
through the Silurian and Devonian, both in Europe and North 
America. It is here confined to the upper beds of the Silurian. 
An inquiry into the number and distribution of the Vic- 
torian species which are also found elsewhere in homotaxial or 
closely-related strata, affords some interesting data. There are 
no less than eleven species of Silurian bivalves (18 per cent.) in 
our Victorian rocks which can be identified with fossils found in 
other, often widely separated areas. Regarding the occurrences 
of similar fossils in Great Britain, shown by the subjoined table, 
it will be noticed that, with few exceptions, the distribution 
ranges through the Wenlock and Ludlow series, whilst in Ger- 
many and Bohemia the fossils occur in the Lower and Middle 
Devonian.* The species of bivalved mollusca which occur in 
North America are found in the Middle Devonian, but not 
below it, whilst one of our forms is also found there in Upper 
Devonian rocks. From this the inference may be drawn, that 
since both in Western Europe and Australia the species made 
their first appearance in the Silurian, the point of dispersal 
would probably be situated mid-way between those places, pro- 
vided the conditions were equal, and that there were no barriers 
to their migration. The data given below would also appear to 
imply that considerable obstacles did exist against their dis- 
persal along the radius extending to Eastern Europe (Germany 
* Cf. Barrande, Syst. Sil. Bohéme, Pt. 1, Vol. VI., Acéphalés, 1881, p. 304. (Stage 
F, included in the Silurian by Barrande, is now referred to the Lower Devonian.) 
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