NUCULA. 215 



Jated, a ligamental fossette at the angle, and a range of 

 comb-like, small, sharp teeth on each side ; ligament chiefly 

 internal. Pallial impression entire. 



Animal subtrigonal, its mantle freely open, without 

 siphonal tubes and with plain edges. Foot deeply grooved 

 and forming an ovate pedunculated disk with serrated 

 edges. One in each pair of labial palps long, curled, linear 

 and fimbriated at its margins ; the other short and fili- 

 form. 



The Nucula are beautiful little bivalves, remarkable for 

 their clean and often glossy aspect and quaker-like hue of 

 their coats. They live in sand or mud, and are never fixed. 

 They inhabit all depths of water, from near tide-marks 

 down to the deepest regions in which Mollusca have been 

 found. The species are sparingly distributed throughout 

 the seas of both hemispheres, and the genus, geologically, 

 ranges back to the oldest fossiliferous strata. We adopt 

 the group as restricted by M oiler. 



Dr. Carpenter has examined the microscopic structure 

 in our commonest British species of this genus, and finds 

 the inner layer of the shell to present a truly nacreous 

 structure ; in the outer a smaller amount of tubular struc- 

 ture may be observed. 



N. nucleus, Linnaeus. 



Never rayed ; epidermis not lustrous ; hinder extremity blunt, 

 its dorsal area not sculptured ; inner margin crenated. 



Plate XL VI I. fig. 7, 8, and (Animal) plate P. fig. 4. 



Area nucleus, Linn. Syst. Nat.ed. 12, p. 1143 (in part). — Pennant, Brit. Zool. 

 ed. 4, vol. iv. p. 98 (probably). — Donovan, Brit. Shells, vol. 

 ii. pi. G3, side figs. — Maton and Rack. Linn. Trans, vol. viii. 

 p. 9o. 



