SILURIAN BIVALVED MOLLUSCA OF VICTORIA. 
A ffinities.—This species resembles in outline NV. 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 Rnow at present, V. melbour- 
nensis is confined to the neighbourhood of Melbourne. 
Horizon and Locality—Silurian (Melbournian). Yarra 
Improvement Works, 8. Yarra; Sewerage Works, Domain road, 
S. Yarra; Swanston-street Sewer, Melbourne; also a doubtful 
specimen from Merri Creek, Kalkallo (Kinlochewe). Coll. Geol. 
Surv., Vict., B> 3. [7895 (type), 7896-8, 985-6. ] 
Nucula umbonata, sp. nov. Pl. IL., 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. 
A ffinities—Both in the general form of the shell and its 
surface ornamentation our species shows some relationship with 
N. varicosa, J. Hall,t 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 are not prominently directed forward. 
Horizon and Locality—Silurian (Melbournian). Type 
specimen from the Police Paddock, Kilmore; coll. Geol. Surv., 
Vict., Bb 22. Also from the south end of the Reservoir, Yan 
Yean; coll. Geol. Surv., Vict., B>- 14. [7899 (type), 7900.] 
*See J. Hall, Pal. N. York, Vol. V., Pt. I., 1885, Lamellibranchiata IT., p. 318, Pl. 
XLVL, Figs. 1-9. 
¢ Pal. N. York, Vol. V., Pt. I., 1885, Lamell. II., p. 319, Pl. XLVI., Figs. 12-23, 
Pl. XCIII., Fig. 4. 
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