Upper Silurian.] PALMONTOLOGY OF VICTORIA. [ Mollusca. 
thirds the length towards the deflected edge, which latter bears numerous fine, 
nearly straight, linear, simple or once-branched pallial impressions, about twice the 
size of the external strie; inner surface of both valves with small spinulose 
tubercles; cardinal area moderately large in both valves. Average width of flat 
rostral portion at cardinal angles 1 inch 3 lines; proportional width of ditto at 
middle, 742; ; length of ditto, °%;; length of deflected front, 4%5,. 
REFERENCE.— Conchita rhomboidalis (Wilckens) (1769) Nachricht = Anomites 
rhomboidalis (Wahl.), Nova Acta Upsal, vol. viii. (1821)= Productus depressus 
(Sow.) Min. Con, t. 459. = Leptena depressa, Sil. Syst. t. 12, f.2 + L. tenuistriata, 
Sow. Sil. Syst. t. 22, f. 2a + L. rugosa (Dal.). 
In some states of preservation, or partial decomposition, each of 
the longitudinal striz seems divided into two, giving rise, I have 
no doubt, to the species L. tenwistriata (Sow.), but by far the 
greater number of specimens in the Caradoc and Bala rocks only 
show, on accurate measurement, the same number of striz in a 
given space as the Wenlock specimens. Some specimens in which 
the front is gradually rounded into the sides, agreeing with 
LL. rugosa (Dal.), differ in no other respect from the normal 
specimens, and the passage is so gradual and obviously unim- 
portant, that I have no doubt of the specific identity of the forms. 
Some specimens have the muscular impressions narrower, and the 
dental lamelle diverging at a less angle than above, and varying 
in length from little more than one-third to nearly two-thirds the 
length of the visceral disk. The variety with wide muscular 
impressions has them varying also from less than one-half to more 
than one-half the length of the visceral disk. These varieties do 
not at all accord with any of the changes of form or striation 
noted ; nor is there any relation between the fineness of the 
striation and the geological position, although, generally speaking, 
the fine striation is most common in specimens from the old beds. 
I cannot find the slightest difference in the number of striz in a 
given space, or in any of the other characters, between the 
European Silurian examples and those occurring in the rocks of 
corresponding age in Victoria. 
Common in the Upper Silurian (Wenlock shale) at Yering, 
Upper Yarra. 
EXPLANATION OF FIGURES. 
Plate XLVI.—Fig. 1, specimen of receiving or dental valve, natural size (one side 
imperfect, but made up by dotted lines), 
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