1 5 2 Shell Life 



coloured cartilage is covered by a chalky band 

 (ossicle) free from the shell, and a strengthening rib 

 runs from under the beaks towards the centre of 

 the siphon-outlet. It has been taken from deep water 

 (12 to 90 fathoms) in muddy sand, off various parts 

 of our coast, but chiefly Scotland and north-west 

 England. The Short Basket-shell (N'. ahhreviata) 

 is almost transparent and extremely fragile, of a 

 triangular-oval shape, swollen, and the valves almost 

 equal. The surface is slightly glossy, ornamented 

 by about a dozen concentric folds, and a curved 

 sharp rib wliich runs from behind the beak. It 

 is greyish in colour, covered by a yellow-brown 

 epidermis. It has been taken chiefly in deep 

 water (40 to 75 fathoms), oflP muddy ground, in 

 Loch Fjaie and around Shetland and Sk^^e ; though 

 in the Kyles of Bute it has been found in 18 fathoms. 



The Fine - ribbed Basket - shell (N. costellata) is 

 similarly semi-transparent and fragile with the 

 previous species, but is much smaller, less swollen, 

 the valves less equal, marked with from 20 to 30 

 fine ribs radiating from the beaks. It has been 

 taken with the last mentioned, of which it may 

 be only a variety. 



Anotlier small genus of this order is known as the 

 Otter-shells (Liitrarla), of which we have two species. 

 The shells gape at each end like those of the 

 Gapers, and the long siphons are similarly covered by 

 a coarse epidermis ; but there are differences in the 

 hinge-teeth which separate Lutraria from My<(, that 

 of the Otter-shells closely resembling the cardinal 

 teeth of the Trough-shells {Mo.ctra). There is a 

 spoon-shaped hollow for receiving the cartilage in 



