NUCULA. LEDA. 71 
N. radiata of authors is beyond doubt the “ nucleus,’ 
is the N. decussata. We have examined the animals of the 
three, and they are absolutely identical. The Exmouth variety 
of the “ nucleus,’ termed “ decussata,’ does not attain so large 
a size as the Irish examples, but I challenge the most acute 
observer to point out an essential conchological variation ex- 
cept the one stated. 
? and so 
N. nitipa, Sowerby et Auct. 
N. nitida, Brit. Moll. ii. p. 218, pl. 47. f. 9. 
The organs of this species are similar in essentials to those 
of the N. nucleus. We may state, the specific distinctions are, 
that the foot is of much paler colour, and the disk less deeply 
dentated; the branchize are paler and smoother on the outer 
surface, but more striated on the inner, than in the N. nucleus. 
It inhabits in company with its congener, but is twenty times 
more rare. 
N. tenuis, Montagu. 
N. tenuis, Brit. Moll. ii. p. 223, pl. 47. f. 6; (animal) pl. P. f. 5. 
We have not seen it alive; it is a Scotch production. 
LEDA, Schumacher. 
L. caupata, Donovan et Auct. 
L. caudata, Brit. Moll. ii. p. 226, pl. 47. f. 11, 12, 13; (animal) pl. P. 
tere: 
Arca minuta, Auctorum. 
We can say little of this genus except that it appears to 
differ from Nucula in having the mantle produced into two 
siphons of moderate length, partly united, but bifurcating at 
their terminations. We have only rarely taken the dead shells 
of this species at Exmouth. It is an abundant Scotch pro- 
duction, and differs much in the outline and markings. 
L. pyemaa, Minster. 
L. pygmea, Brit. Moll. i. p. 230, pl. 47. f. 10; (animal) pl. P. f. 3. 
This species, if distinct from the L. caudata, is mknown to 
