Upper Silurian.) PALZZONTOLOGY OF VICTORIA. (Mollusca. 
narrowness of the front: 3rd, in the number, thickness, and 
closeness of the ridges, and the scales which cross them, both of 
which are often smaller and closer than the above-described 
typical variety. The beaks are sometimes so close that the 
cardinal area, small perforation, and deltidium in the larger valve 
cannot be seen ; in other specimens they are all distinct. 
This is one of the few fossils clearly common to the Silurian and 
Devonian formations, in both of which it occurs in Victoria, the 
Australian examples being undistinguishable from those of Europe 
in the same formations. Both the fine-ridged variety forming the 
T. affinis of Sowerby, and the variety with broader and fewer 
ridges forming his 4. aspera, occur in the Devonian and Silurian 
rocks of this colony. 
Abundant in the Upper Silurian strata of Yering, Upper Yarra. 
EXPLANATION OF FIGURES. 
Plate XLVII.—Fig. 1, view of larger valve of average or rather small specimen, natural 
size. Fig. la, front end view of same specimen, showing the wave in the margin. Fig. 1, 
rostral end view of same specimen. Fig. le, portion of surface magnified to show the strong 
scaly lamine of growth crossing the longitudinal ridges. Fig. 2, view of interior of another 
specimen, showing the muscular impressions, natural size. 
Piate XLVII., Fias. 3, 4, 5, 6. 
RHYNCHONELLA (HEMITHYRIS) DECEMPLICATA 
(Sow. ). 
[Sub-genus HEMITHYRIS (»’Orz.). (Sub-kingd. Mollusca. Class Palliobranchiata. Order 
Brachiopoda. Fam. Rhynchonellide.) 
Gen. Char.—F oramen triangular, not separated from the hinge ; beak acute, pointed, entire ; 
no cardinal area ; entering valve with a small mesial septum ; apophyses short, arched, triangular, 
with small dental lamelle ; two strong diverging cardinal teeth bordering the opening in the large 
valve, supported by dental lamellz, extending to the inner surface of the valve.] 
Description. —Sub-rhomboidal, apical angle 115°; both valves moderately 
convex ; mesial ridge and hollow very large and sharply defined, forming an abruptly 
defined angular sinus in the front margin, nearly as high as wide, bidentate by two 
strong angular ridges on the entering valve, and one very much smaller in the 
middle of the sinus of the receiving valve; lateral ribs sub-angular, rather smaller 
than the mesial ones, five to seven (but usually six) in number, all continued simply 
to the beak; surface crossed by fine transverse lines of growth. Average width (of 
small specimen), 53 lines ; proportional length, »%3,; length of entering valve, 15%. 
REFERENCE.— Terebratula decemplicata, Sow. Sil. Syst. t. 21, f. 17. 
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