NUCULA. LEDA. 71 



N. radiata of authors is beyond doubt the " nucleus," and so 

 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. 



N. NITIDA, Sowerby et Auct. 

 N. nitida, Brit. Moll. ii. p. 218, pi. 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 branchise 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. tennis, Brit. Moll. ii. p. 223, pi. 47. f. 6; (animal) pi. P. f. 5. 

 We have not seen it alive ; it is a Scotch production. 



LEDA, Schumacher. 

 L. CAUDATA, Donovan et Auct. 



L. caudata, Brit. Moll. ii. p. 226, pi. 47. f. 11, 12, 13; (animal) pi. P. 



f. 2. 

 Area 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. PYGM^A, Minister. 



L.pygmeea, Brit. Moll. ii. p. 230, pi. 47. f. 10; (animal) pi. P. f. 3. 

 This species, if distinct from the L. caudata, is unknown to 



