86 AMERICAN JOURNAL 



names elodcs^cataseopium^emargiiiata^fragiUs^ka., seem thus 

 far to add nothing to the observations of others. In fact, the 

 soft 'parts of all these are too slightly varied to admit of a suspi- 

 cion of specific difference. We are left then to consider the 

 forms and appearances of the shells ; and those for any of the 

 supposed species referred to above exhibit a succession of varia- 

 tions that blend the whole mass into one. The presence or ab- 

 sence of ferruginous or other coloring matter determines the 

 color of the shell in a remarkable degree. The temperature of 

 the water determines the mode of development of the shell in a 

 very obvious manner ; abundance or scarcity of food will deter- 

 mine in a remarkable manner the size of the soft parts, and of 

 course that of the enclosing shell. Whether the whorls of a 

 shell be regularly and symmetrically rounded, or on the other 

 hand assume a malleaied appearance, as if little plane facets had 

 been formed on a soft convex surface by hammering, is not a 

 specific character. It depends upon the rapidity of the growth 

 of the soft parts, and whether there be at the same time a sufii- 

 cient amount of calcareous matter in the food of the mollusc to 

 give the shell a sufficient solidity not to yield to the external in- 

 fluences by which the mollusc is surrounded. 



I have often taken L. elodes while in rapid growth, and found 

 the margins of the shells so thin and fragile that the slightest 

 handling would fracture them. In all such cases the appearance 

 of the surface of the shell is of the character called " malleated." 

 We do not often find this appearance in those shells we call 

 catascopium, for the reason that the shells so called are generally 

 found in bodies of water of very equal temperature, often rapidly 

 moving; food is also less abundant, and the growth of the soft 

 parts is not so rapid but that the whorls of the shell retain their 

 rotund form. It may be suggested, then, that the following 

 differences in station account for»the supposed species that pro- 

 bably are in reality only one : 



An equable temperature, a moderate supply of food, limited 

 supply of air, and frequent disturbances of the station of the 

 animal by currents in the water, determines the form we call 

 catascopium. 



A warmer station, abundance of food, unlimited access to the 

 atmosphere, and quiet stagnant water, favor the developuient 

 called elodes. 



In the instances I have referred to in my papers in the Pro- 

 ceedings of the Bost. Soc. Nat. Hist, and in the Amer. Jour. 

 Conch., the eggs o{ catascopium were developed as elodes by be- 

 ing transferred to a shalloiv stream, wliere they found favoring 

 conditions in the rich confervoid vegetation growing in the inter- 



