SILURIAN BIVALYEU MOLLUSCA OF VICTORIA. 
preservation, as it seems to have been partly decorticated. 1 he 
tegulate ornament on the sharp costae towards the base of the 
shell appears exactly as shown in McCoy’s drawing. There 
seems to be no reason for doubting the generic affinity of this 
species, although queried by McCoy. In his Fossils of the 
British Islands, Robt. Etheridge refers* to the genus without 
a query, but misquotes the specific name as “ acuticosta.” 
Horizon and Locality. — Silurian (Yeringian). Cave Hill, 
Lilydale. Collected by the author. [2268.] 
Genus Mytilarca, J. Hall, 1873. 
Mytilarca acutirostris, sp. nov. PI. IV., Fig. 67. 
Description. — (Cast). Small, ovate, sub-trigonal; length 
slightly less than the height. Anterior and basal margins 
curved and meeting almost at right angles; posterior margin 
truncate and broadly curved. Beaks acuminate, curving 
sharply forward. Cardinal grooves presenf on the anterior 
and posterior ligamental areas. An anterior umbonal ridge 
passing immediately below the beaks to the ventral margin. 
Highest part of valve just behind this ridge. Surface of shell 
gently curving from the beaks to the base and truncated 
posterior margin, steeply falling to the anterior border, where 
it is depressed, and continued so along the base. Inner surface 
markings consisting of numerous, indistinct, concentric growth 
lines seen as shallow sulci. 
Measurements. — Length, 9 mm.; height, 10.5 mm. 
Affinities. — The present species differs from Mytilarca 
[“ Cardium ”] trigona, Goldfuss sp.t in having the beaks more 
incurved, and a more rounded basal margin. " Another species 
which seems to bear some relation towards ours is Salter’s 
Mytilarca [“ Mytilus ”] chemungensis ( non Conrad), from the 
Wenlock Shale of Usk, Wales.}: This is, however, a more 
generally elongate form. 
Horizon and' Locality. — Silurian (Yeringian). Coll. Geol. 
Surv. Viet., from junction of the Woori Yallock and Yarra 
B 23. [7930.] 
*Vol. i., 1888, p. 99. 
t Petrefactise Germanise, Vol. II., 1837, p. 215, PI CXLII Fi<rs Sac 
X Mem. Geol. Surv. Gr. Brit., Vol. II., Pt. I., 1848,’ p. 365, PI. XX., Figs, 10, u. 
