SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
Affinities. — This species resembles in outline N. bellistriata, 
Conrad, sp., # from the Hamilton Group of N. America, but lacks 
the fine concentric sculpturing of the surface seen in the latter. 
Observations. — N. melbournensis is variable in outline, and 
although agreeing in general form, a series can be readily 
collected which shows a regular gradation from narrow-oblong 
to broadly-ovate, or even sub-orbicular forms. It is abundant 
in some of the localities around Melbourne, especially in the fine 
argillaceous shales. So far as we lvtiow at present, A. melbour- 
nensis is confined to the neighbourhood of Melbourne. 
Horizon and Locality. — Silurian (Melbournian). Yarra 
Improvement Works, S. Yarra ; Sewerage Works, Domain road, 
S. Yarra; Sw an ston -street Sewer, Melbourne; also a doubtful 
specimen from Merri Creek, Kalkallo (Kinlochewe). iColl. Geol. 
Surv., Viet., B b 3. [7895 (type), 7896-8, 985-6.] 
Nucula umbonata, sp. nov. PI. II., Figs. 34, 35. 
Description . — Shell sub-trigonal, oblique; strongly convex, 
especially toward the beaks. Ventral margin gently rounded; 
anterior border widely curved, sloping steeply and sub-truncated 
at the junction with the ventral margin; the posterior border 
is formed by a long curved slope, meeting the ventral margin 
somewhat abruptly. Beaks not very prominent, incurved, 
gibbous. Umbonal slope narrowly rounded, extending from the 
beaks to the postero-ventral margin. Surface of shell marked 
by several strong concentric varices, between which occur 
numerous fine growth lines. One specimen shows the ligament- 
pit (resilifer) very clearly. 
Measurements. — Length, 11 mm.; height, 9 mm.; depth of 
valve, 3.5 mm. 
Affinities. — Both in the general form of the shell and its 
surface ornamentation our species shows some relationship with 
N . varicosa, J. Halt,! a fossil from the Hamilton Group of N. 
America (N. York State). A marked difference, however, exists 
between them, in that the Australian species has sub-anterior 
beaks which arc not prominently directed forward. 
Horizon and Locality. — Silurian (Melbournian). Type 
specimen from the Police Paddock, Kilmore; coll. Geol. Surv., 
Viet., B b 22. Also from the south end of the Reservoir, Yan 
Yean; coll. Geol. Surv., Viet., B b - 14. [7899 (type), 7900.] 
* See J. Hall, Pal. N. York, Vol. V., Pt. I., 1885, Lamellibranchiata IT., p. 318, PI. 
XL VI., Figs. i-q. 
f Pal. N. York, Vol. V., Pt. I., 1885, Lamell. II., p. 319, PI. XLVI., Figs. 12-23, 
PI. XCIII., Fig. 4. 
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