SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
behind. Height nearly equal to the length. Beaks prominent, 
sub-central, slightly anterior, and directed forward. Surface 
of shell not much inflated, with the greatest convexity towards 
the middle; ornamented by about 10 flattened riblets on the 
median area, each having towards the ventral border a distinct 
groove, becoming evanescent beyond half the length. Postero 
dorsal area bearing a few riblets, disappearing toward the 
beaks. 
Measurements.-— Length of the type specimen, 4.25 mm. ; 
height, 4 mm. 
Observations. — This form might be regarded as the imma- 
ture shell of P. gippslandica, but for the distinguishing feature 
of the riblets, which are depressed and grooved, whilst in P. 
gippslandica they are simply and sharply ridged. 
Affinities. — -The nearest related form to the above appears 
to be Barrande’s Panenka nana* from Stage E in Bohemia. 
The chief differences shown in the latter are the more numerous 
riblets, the narrower interspaces, the double striae on their sur- 
faces, and the general form of the shell, which is not so 
depressed; neither are the alee so well developed as in ours. 
Horizon and Locality. — Silurian (Yeringian). In the dark 
shale of Mt. Matlock, associated with Tentaculites mattock - 
iensis, Chapman;! presented by Mr. N. Lepoidivil, in 1877. 
[7879.] 
Panenka cingulata, sp. nov. PI. I., Eig. la. 
Description. — Shell of medium size, obovate, ventral border 
evenly rounded, abrupt in front, produced behind. Surface 
evenly convex in the median area and near the umbones; concave 
anteriorly, depressed posteriorly. Beaks oblique, pointing for- 
ward. Surface ornament consisting of about 26 curved ribs 
radiating from the umbo, well-rounded, closely set and separated 
by deep furrows. The ribs are transversely crossed at intervals 
by the rather deep concentric furrows, which apparently repre- 
sent distinct stages in the growth of the shell, causing 
interference with the continuous and even growth of the riblets 
Measure ments. — Length , 38 mm.; height about 26 mm,; 
greatest depth of valve, 5 mm. 
Observations. — The regular convexity of the valves, and the 
rounded ribs render this form easily distinguishable' from P 
gippslandica, McCoy. 
* Syst. Sil. TSolieme, Vol. VI., Pt. I., Acephales, 1881, PI. i ro , Vies i ,• 
Figs, i., 4-7- g , 3 ’ 
t Proc. Roy. Soc., Viet., Vol. XVI. (new series), Pt. II., 1904, p 3,8 PI 
Figs. 1, 2, 3, 5. 
PI. 266, 
XXXI., 
1 22 ] 
