LUCINA. 83 
what closed anteriorly and posteriorly, leaving a large pedal 
opening in the centre of the ventral range; no siphonal pro- 
cess appears, not even an orifice; the branchize must be sup- 
plied through the pedal aperture. The body is very small, 
pale brown, with the intestine passing through the liver. There 
are two subquadrangular branchiz, and two palpi, on each 
side; the former are finely pectinated above, and smooth on 
the under surface ; the palpi are moderately long and pointed, 
as well as striated on one side; both are of a good brown 
colour. The foot is clear white, moderately long, flattish, and 
lanceolate-shaped laterally and at the point. 
The L. rotundata has been consigned to a new genus, termed 
Diplodonta, by the learned authors of the ‘ British Mollusca,’ 
on our authority as to the animal structure. I feel pleasure 
that they state this allocation is provisional, as the animal 
presents anomalies of so peculiar a nature, that malacologists 
are earnestly called on for a minute examination of this curious 
creature. I accept the invitation, and hope either to confirm 
my observations, or offer rectifications. This species has many 
of the characters of the type, L. borealis, and I think, whether 
my notes are confirmed or not, it must be considered an out- 
lying branch of this family. The hinge and other distinctions 
will not, in any case, allow of the suggestion of handing over 
this species to the Kelliade. 
Fresh, though dead shells are commonly taken in the coral- 
line zone at Exmouth, but I never met with more than two 
specimens alive; the one examined was less than half an inch 
diameter. 
The followmg addenda were made at Exmouth on the 22nd 
July, 1850, a year after the preceding notes. The account im 
the ‘ British Mollusca,’ vol. 1. p. 65, of the Diplodonta rotun- 
data, our Lucina rotundata, was made from the sketch above. 
The possession of a live specimen of } of an inch diameter, 
enables me to say that my account, as far as it goes, is nearly 
correct; but I can offer some amplifications, particularly on 
that important organ the foot. Beyond all doubt, I state, 
that there are, on each side, a pair of branchiz and palpi; 
the branchiz are transverse, though somewhat elongated, 
Gaz 
