227 
‘domei form. It is not explained by senility, for in young 
individuals an equal disparity is seen. 
It may attain a height of 50 mm., a length of 51 mm., 
and a section of 35 mm. 
The ribs differ. Generally they are broad and rounded, 
wider than the interspaces, which are deep and flat, with 
vertical sides. But sometimes the ribs are low and wide, and 
touch one another, so as to have no intervening squarely- 
ploughed furrow. The concentric sculpture usually consists 
of flattened contiguous plates on the ribs, while in the inter- 
costal spaces there are low, vertical, thin lamellae. But it 
may be no more than crowded concentric lire, both on the 
coste and between them. 
The “lunular area” referred to by Angas is on the pos- 
terior side of the shell, and therefore does not correspond 
with the lunule of such shells as Chione. It may be very 
defined, or only slightly marked or absent. 
Not a few individuals, after reaching a diameter of 25 
mm., cease to grow in superficial area, but increase in sec- 
tional diameter, while they actually decrease in their umbo- 
ventral; so that their margin becomes curiously incurved and 
their walls very thick, as figured in pl. xxviii., fig. 4. 
As to ornament, some shells in life are nearly white 
without and quite white within; others are of an almost uni- 
form cinnamon-brown. The usual colour is a dirty-greyish or 
very faint rusty tint, with rather reddish-rusty indistinct 
blotches, disposed in irregular and broken cencentric lines ; 
but they.may have a pure white-ground colour, marked with 
long radial, dark purple-brown spots, variously disposed in 
patterns, or scattered, or coalescing into a large area over 
the ventral part of the posterior half of the shell. 
So within, some are quite white; others have a dark- 
brown line along the pallial margin, and edging each adduc- 
tor scar; others have the muscle-scars and the greater part 
of the interior of a dark purple-brown. 
The extent to which the muscle-scars, anterior or pos- 
terior, are supported by a callosity also differs greatly. 
There is every combination of the above-named differ- 
ences, so that no true varieties can be established : only in- 
dividual variations are recognized. 
Glycimeris sordidus, Tate, P= AS 
Pectunculus sordidus, Tate, Trans. Roy. Soc. S. Austr., 1891, 
vol. xiv., p. 264, pl. xi., f. 8. Type locality, St. Vincent Gulf, 9 
to 11 fathoms, alive (Verco). I have taken it since in numbers in 
Hardwicke Bay, in Backstairs Passage, and in Investigator 
Strait, at all depchs from 13 to 22 fathoms. 
Professor Tate had only an immature individual from 
