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. 
A ffinities—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 strize on their sur- 
faces, and the general form of the shell, which is not so 
depressed; neither are the alz so well developed as in ours. 
Horizon and Locality—Silurian (Yeringian). In the dark 
shale of Mt. Matlock, associated with Tentaculites matlock- 
iensis, Chapman;t presented by Mr. N. Lepoidivil, in 1877. 
(7879. ] 
Panenka cingulata, sp. nov. Pl. I., Fig. 14. 
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. 
Measurements.—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. Bohéme, Vol. VI., Pt. I., Acephalés, 1881, Pl. 110, Figs. 1-3; Pl. 266, 
Figs. I., 4-7- / f 
+ Proc. Roy. Soc., Vict., Vol. XWI. (new series), Pt. II., 1904, p. 338, Pl. XXXI., 
IME lin Sey eh Ty 
