186 
This valve is considered ventral, because the broken surface in 
the umbonal region indicates that ieee had been a small, slightly- 
elevated beak. 
Dimensions.—Length of hinge-line, 20; umbo-ventral diameter, 
11; greatest vertical depth of medial furrow, 7 millimetres. 
Locality. —Cambrian limestone at Parara, near Ardrossan (one 
valve). 
PTEROPODA, 
Salterella planoconvexa, spec. nov. Plate ii., figs. 3-30. 
Salterella sp., Tate, Trans. Roy. Soc. 8. Aust., 1890, p. 249. 
Test rather thick, externally finely and closely wrinkled- 
striated transversely. Shell broadly conical, tapering to an acute 
point ; plano-convex in a medial transverse section ; lateral mar- 
gins rounded or subangulated... Dorsal surface convex, but 
towards the apex marked witha shallow medial depression 
bounded by broad obscure ridges. Ventral surface with a broad 
shallow medial depression, more conspicuous in the apical region. 
A natural longitudinal fracture discloses two invaginated septa, 
and a transverse section near the apex one invagination. 
Dimensions of a moderate-sized example :—Length, 28 ; dorso- 
ventral diameter, 7 ; lateral diameter, 10 mills.; but the pro 
portionate measures of the diameters are variable. The longest 
example measures 35 mm. in length. 
Locality.—In the Cambrian limestones at Curramulka. 
This species has an external resemblance to Hyolithes Billingsi, 
Walcott, which is described as possessing flat transverse septa. 
S. Hardmanni, Etheridge, the only described Australian species 
of the genus is elongate-conical, with a circular transverse 
section, and consequently i is far removed from S. plano- convent, 
which seems to stand alone among congeners. 
Hyolithes communis, Billings. Plate ii., fig. 2 
Ref:—Hyolithes communis, Shaler and Foerste, Bull. Mus. 
Comp. Zool., 1888, t. 2, f. 23, p. 34; ad., Walcott, Tenth Annual 
Report, U. States Geol. Surv., 1890, t. 77, figs. 3 and 4. 
Shell straight, gradually tapering, marked by fine transyerse 
striz and concentric ridges ; the transverse sections are circular 
or slightly oval. 
Locality.—Cambrian limestones at Curramulka. 
Hyolithes econularioides, spec. nov. Plate ii., figs. 1—la. 
Shell straight, elongate, tapering to an acute point, apical 
angle about 20°; lateral angles sharp. The dorsal and ventral 
surfaces similar (?); each with two elevated subacute ridges 
separated by a deep concave medial furrow, the slope from the 
ridges to the lateral margin moderately steep. Posteriorly the 
