SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
Nucula arceformis, sp. nov. Pl. I1., Fig. 36. 
Description.—Shell sub-rectangular, oblong; strongly 
convex toward the beaks, sloping away toward the ventral 
margin, which is depressed and almost flange-like. Beaks 
prominent, sub-central, directed slightly forward. Both ex- 
tremities vertically truncate and only slightly rounded; ventral 
margin straight. Surface marked by irregular and somewhat 
coarse undulations or lines of growth, especially conspicuous 
near the ventral border. 
Measurements.—Length, 15 mm.; height, 10 mm.; depth of 
valve, about 2.5 mm. 
Affinities —The shape of the valve in this species is pecu- 
liarly rectangular, and not quite comparable with any form 
hitherto figured, the nearest being Nucula subequalis, McCoy, 
sp.,* from the Upper Llandovery beds of the Malverns and 
Wales. The latter species, however, is much more gibbous in 
the umbonal area. A fragment of another valve is fortunately 
found underlying the figured specimen of N. arew@formis, which 
shows the form of hingement to belong to the genus Nucula. 
Horizon and Locality —Silurian (Melbournian). In the hard 
black shale of the Domain-road Sewer, and the blue mudstone 
of the Yarra Impt. Works, 8. Yarra (coll. by F. P. Spry). Also 
from Merri Creek, sect. XX VIII., parish of Merriang, and hills 
east of Creek; coll. Geol. Surv., Vict., B> 6. [7901 (type), 
7902-6. | 
Nucula taylori, sp. nov. Pl. IL., Figs. 37, 38. 
Description—Shell small, sub-ovate. Beaks prominent, 
incurved, sub-acuminate, sub-central. Cardinal Ime strongly 
arched. Ventral margin gently and evenly rounded, curving 
boldly anteriorly, and sharply at the posterior extremity, where 
it is truncated toward the beaks. A well-marked umbonal 
slope runs from the beak to the postero-ventral margin. 
Cardinal area on both sides of beak depressed. Surface smooth, 
or with a few faint lines of growth. 
Measurements.—Length, 6.5 mm.; height, 5 mm. 
Affinities —N. taylori bears some resemblance to Mxcula 
anglica, VOrbigny,t which ranges from the Caradoc series to the 
Lower Ludlows in Britain; the chief difference being the greater 
convexity of our form, especially in the umbonal region. 
*(Arca subwqualis) Brit. Pal. Fossils, p. 283, Pl. rK., Fig. 1. Siluria, 4th ed., Pl. 
Xb Hugsig7n ee - : 
+Prodr. Pal., p 33, Stage 1, No. 194. Nucla ovalis, Sowerby, Sil. Syst., 1839, 
Gog, Pl. V., Fig. 8. Ctenodonta anglica, d’Orb. sp. Siluria, 4th ed., 1867, Pl. XXXIII., 
p- 
Fig. ro. 
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