GYPR^A. S» 



completion of his first shell. We find^ in general, 

 that in the construction of the Univalves, the whorls 

 increase in magnitude as they advance transversely 

 from the apex, and receive no increment after the 

 perfect aperture is formed. This bespeaks a limit 

 in the growth of the inhabitant, at which he is 

 taught by instinct to finish oif his work. If there- 

 fore, for any reason, upon which from ignorance 

 we cannot argue, these slugs do quit their shells, 

 it is not, surely, on account of an anomalous 

 excess of bulk. A remark which has been made 

 by the author, whether justly or not will hereafter 

 be decided, would seem to favour a very opposite 

 opinion. In numberless specimens of the Cypraea 

 exanthema which he has inspected, the thinner 

 and obviously younger shells were, with few ex- 

 ceptions, of large dimensions, whereas the fully 

 ocellated and thicker individuals were consider- 

 ably smaller. So much difference is there usually 

 in size, that they might be considered as two 

 distinct varieties, were not a progressive course 

 easily obtained, from those having broad bands 

 alone, to those covered with white spots and to- 



