SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
the molluscs found time and material for forming a broad 
varix along the pallial border; whereas in sandy areas or under 
impure conditions of the water, as, for instance, in the presence 
of decaying Crustacea and cephalopoda, seen in the JDomain- 
road examples, the successive laminae were laid down closer 
together, and the shell itself would be proportionately thin and 
depauperated. 
This, together with another newly-described ornate species, 
P. producta, are among the commonest forms of the genus in the 
Victorian rocks. 
Affinities. — P. victoria somewhat resembles the type ot 
shell described under the name of P. muta by J. Hall,* from the 
Hamilton Group of the State of N. Aork. P. muta differs, 
however, from our species in having the beaks decidedly anterior, 
in the extremely lamellose condition of the main concentric 
striae, and in the absence of the eoncavely depressed escutcheon 
in the posterior region. 
Horizon and Locality . — Silurian (Melbournian). From the 
Yarra Improvement Works, S. larra, in blue and yellow shale, 
common; in the hard, dark shale oi the Domain-road Sewerage 
Works at 103 ft. from surface, presented by Mr. F. P. Spry. 
In the yellowish sandstone with casts of shells, coll. Geol. Surv. 
Viet., Moonee Ponds Greek, Flemington; in the brown argil- 
laceous rock of Broadhurst’s Creek, east of Kilmore, coll. Geol. 
Surv. Viet., B b 18. In the brown argillaceous sandstone of 
Anderson’s Creek, near Warrandyte, coll. Geol. Surv. Viet., 
Bdd , m the sandstone of Frasers, or Vo. 3, Creek, Springfield 
coll. Geol. Surv. Viet., B b 25. [7915 (type), 7916-7 ] & 
Palceoneilo raricostce, sp. nov. PI. IH fio’ 50 
Description — Shell of variable size, length more than twice 
the height, elongate-ovate, rostrate. Depressed convex 
Umbonal ridge not strongly developed. Anteriorly broad and 
well-rounded, the margin meeting the cardinal line at an obtuse 
angle; posteriorly produced and sharply rounded Cardinal 
line arcuate straight between the vertical line and the posterior 
angle. Beaks depressed Teeth of hinge characteristic, but 
comparatively large and few. Greatest convexity of shell 
surface just behind the anterior umbonal slope * Shell 
mented with well-marked lamelliform concentric varices, com- 
paratrveiy widely spaced, the area between each being relieved 
by numerous thread-like strise. 8 
* Palaeont. N. York, Vol. V., 
[ 34 ] 
