Lamarck's Genera of Shells. 65 



Shell inflated, oval, ventricose in the middle, smooth, milk white ; 

 extremities rather prominent, subtruncated ; mouth orange. Mo- 

 luccas. PI. v. Fig._203. 12 Recent species, and 2 fossil. 



2. Cypraea. 



Shell oval, or oblong oval, convex on the upper part, somewhat 

 flattened at the under ; lips curved inwards. Aperture longi- 

 tudinal, narrow, indented on both sides, effuse at each end, and 

 extending the whole length of the shell. Spire very small, scarcely 

 perceptible. 



The cypraeae are generally smooth shining shells, agreeably 

 coloured, and without any epidermis. They are remarkable for the 

 different appearance which the shell of the same individual as- 

 sumes at different periods of its growth. In the mature state, these 

 shells answer the description given above, but when young, they 

 have a very different form. The aperture is then more dilated, 

 especially at the lower part, is entirely without indentations, and 

 the right lip is sharp. In its next, or middle, stage of growth, it 

 acquires the general form of the adult shell, but is still incomplete, 

 having only its first superimposed layer of testaceous matter, and the 

 spire, though very small, is not yet entirely covered; its colours, 

 moreover, are still wanting. The second layer of testaceous matter, 

 variegated with the brilliant colours that adorn this genus, is de- 

 posited by two membranous expansions of the mantle of the animal, 

 which it spreads over the back of the shell, so as to cover and con- 

 ceal it completely, thus adding at once to its solidity and beauty. 

 In some species, the place where the two edges of the mantle 

 meet, is marked by a longitudinal line, on the back of the shell, 

 of a different colour from the rest of it. 



From the varying form of this shell, accoiding to its age, we 

 must be careful to distinguish the three separate states in which it 

 is likely to be met with, or we shall be liable to mistake the same 

 individuals for three distinct species. 



In some species the place of the spire presents a little pit, simi- 

 lar to an umbilicus, in others it is almost obliterated. In like- 

 manner the two external margins of the shell are sometimes both 



Vox.. XVI. F 



