INTRODUCTION, Panama Shells. 25 



Ocean, New Holland, &c., we may often suspect the error to 

 arise more or less from erroneous testimony. But when one 

 species is referred to two distinct zoological provinces, which 

 are known to contain analogous but not identical species, we 

 must sometimes suspect the author of confounding such species, 

 if indeed in these cases the difference of the local types were 

 clearly distinguished, it would be of little importance whether 

 or not the difference were considered to be of specific value. 

 But not even after the specimens are deposited in a collection 

 has all danger of error ceased. A misplacement of labels or 

 of shells, which are not properly secured, may lead to 

 erroneous statements of habitat. 



For all these causes of error there is but one remedy, and 

 that is not infallible. Rejecting the testimony of careless 

 and incompetent observers, and all hearsay testimony, we 

 must rely on the testimony of competent observers. "We may 

 hope for accuracy when they shall remember that a very few 

 errors may essentially change the aspect of the plan of dis- 

 tribution, and prevent all correct generalizations. , 



A great amount of valuable materials, for interesting 

 generalizations on the number and distribution of the species 

 of marine MoUusks, has been collected by public and private 

 expeditions. But when we consider the immense profusion 

 of species and of individuals in tropical seas, and the confu- 

 sion of the habitats of many as exhibited in the present 

 literature of conchology, so that the plan of distribution is 

 misrepresented, — that which has been done only stimulates 



may happen in casual coUi.\ ^ ions. By a singular coincidence, only a few days 

 after we had described Helix kedfieldlana (which proves to be H. Cnrmelita Fer.) 

 that inhabits a limited district in Jamaica, a specimen was brought to New-York 

 by a collector, who affirmed that he procured it in California. Subsequently the 

 statement was repeated, but afterwards it was recollected that the shell had been 

 purchased in Kingston, where the steamers stop on theii' homeward voyage. 



1 



