198 Linnaan Society. 



Olive, two genera of Pectinibranchiate Mollusks." By Lovell Reeve, 

 Esq., A.L.S. &c. &c. 



After referring to the numerous instances of very considerable 

 modifications in the form of shell and mode of calcification which 

 occur among Mollusca, even in genera very nearly related to each 

 other, Mr, Reeve proceeds to describe more particularly the manner 

 in which the calcifying process is performed in the two genera which 

 form the subject of his paper. Each of these genera produces a 

 porcellanous shell of very analogous structure, consisting of a cy- 

 linder of several enlarging whorls, convoluted on a plane nearly ver- 

 tical to the spire, and composed of layers of vitrified enamel of dif- 

 ferent colours and design ; but there is a striking diflference in the 

 calcifying organ as regards its structure and its function of secretion. 

 In the Cowry the office of calcification is performed by a lobate ex- 

 pansion of the mantle from either side of the aperture, sufficiently 

 large to cover the entire shell, and retracted only under the influence 

 of alarm. In the Olive, on the other hand, the mantle is limited to 

 the interior and the aperture of the shell ; and appears to be furled 

 over the edge of the lip, and retained in a state of tension by a cord 

 or filament passing from its posterior extremity into a narrow channel 

 which is excavated round the spire of the shell in place of the suture. 

 The result of this difference in the condition of the calcifying organ 

 is, that in the Cowry the testaceous secretion is deposited over the 

 whole shell from the outside in successive layers at different inter- 

 vals of time, while in the Olive the layers must be secreted simul- 

 taneously at the lip alone, and the porcellanous surface of the shell 

 is preserved (both in its course of retrovolution and after maturity) 

 by a reflection of the ventral disc somewhat analogous to the re- 

 flected mantle of the Cowry, but bearing no part in the formation of 

 the shell. 



In support of this view and with the view of proving that this 

 distinction is borne out by the physical condition of the shells at 

 different periods of growth, the author takes for examples Cypreea 

 Tigris and Oliva Utriculus. The Tiger Cowry in its first stage is of 

 a uniform light chestnut-bay ; the colour then breaks up, as it were, 

 into bands of close-set blotches of a richer hue ; a coating of white 

 is next superposed, and upon that is deposited a series of rather 

 distant zigzag flames ; these are partially concealed by a second layer 

 of white enamel thinner and more delicate than the preceding one, 

 on which a number of dark spots are subsequently deposited ; and a 

 third coating of white enamel, with a new layer of black and brown 

 spots intermingled, characterizes the maturity of the shell. Each 

 period in the life of the Cowry appears therefore to be distinguished 

 by a different design of colouring ; but this is not the case with the 

 Olive, the shell of which exhibits the same appearance at all stages 

 of its growth, and the different layers of its colouring matter must 

 be deposited simultaneously because the organ of calcification ex- 

 tends only to the lip, from which the shell gradually recedes in the 

 progress of its growth. The external coating of Oliva Utriculus 

 is of an obscure milky-blue, and the removal of this layer by means 



