SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
Family Ledidae. 
Genus Pal^eoneilo, J. Hall, 1870. 
Palceoneilo victorice, sp. nov. PI. III., Figs. 47-49. 
Description. — Shell of variable size, length more than twice 
the height, rostrate; moderately convex in the umbonal region 
and the triangular area beneath, the latter bounded by the 
anterior slope and the posterior umbonal ridge. Cardinal line 
nearly straight or only slightly arcuate; ventral border sub- 
parallel and straight, but narrowing the shell posteriorly, widely 
rounded anteriorly to meet the cardinal line at an obtuse angle ; 
the hind extremity narrow, with the postero-ventral angle 
bluntly rounded, curving backward and inward to the cardinal 
line, which posteriorly forms a salient angle. Escutcheon well 
marked, the depressed area bounded abruptly by the umbonal 
ridge. Surface of shell gently convex and sloping anteriorly; 
towards the ventral margin the surface slopes more steeply, 
whilst the margin itself, in adult shells, is depressed and flange- 
like. Beaks sub-central or slightly posterior, prominent, some- 
what incurved and depressed, or only moderately inflated. 
Hinge showing an alternating series of curved bars and sockets. 
On the cardinal border there is a well-marked groove to receive 
the external ligament. Surface ornamented with numerous 
concentric lamellar ridges, between which are several parallel 
thread-like striae, whilst, in a very few well-preserved examples, 
traces of fine lineations radiating from the umbo are seen, 
especially stronger on the salient edges of the concentric 
lamellae. 
Measurements . — Type specimen (PI. III., Fig. 47). 
Length, 27 mm. ; height, 12 mm. ; number of concentric lamellae 
in the space of 4 mm., measured in median area — 7. 
A medium-sized example.— Length, 17 mm.; height 7.5 
mm.; number of concentric lamellae in the space of 4 mm. in 
the median area — 9. 
A small example. — Length, 13 mm.; height, 6 mm.; 
number of concentric lamellae in space of 4 mm.— 16. 
Observations . — The number of the concentric lamellar 
ridges to a given width is not a factor of any importance in 
dealing with this group, so far as the Victorian examples show, 
and the various graduations in ornament do not allow of even a 
sub-varietal division of the species. A possible explanation of 
this varying feature in ornamentation, and one partly borne out 
bv the evidence before us is, that in areas of quiet sedimentation 
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6608 .— C. 
