400 T. Bland on the Geographical Distribution of Mollusca. 
may very justly be added,—the confined views entertained by 
authors as to the origin of species. | 
With respect to the first, Dr. Gould remarks truly :— 
“‘ A voyage is made to the Sandwich Islands, and all the shells 
brought home by the vessel are said to be shells from the Sand- 
wich Islands, though they may have been obtained at California, 
the Society Islands, New Zealand, and, perhaps, half a dozen 
other places quite as remote from each other. A sea captain pur- 
chases a collection at Calcutta or Valparaiso, for his friends at 
home ; and all the shells are marked as denizens of the port where 
they were purchased, though they might not have lived within 
thousands of miles. Purchased shells cannot be relied on for 
localities ; for this end a shell must have been found containing 
the animal, or else dredged, or picked up on the shore, and label- 
led accordingly.” —p. ix. 
In support of his view as to the second cause of error, Dr. 
Gould gives various instances, shewing the difficulty which is 
frequently experienced in the detection of specific differences, and 
offers remarks deserving the anxious attention of conchologists. 
e writes :— : 
“When, therefore, we have before us shells from widely diverse 
regions, apparently identical, they should be subjected to the 
most careful scrutiny for structural differences. If no obvious 
ones are detected, we may not consider the question as settled, 
unless the animals have been compared; and we may go even 
further, and require that their internal structure, as well as ex- 
ternal features, should be examined. The number of instances 
where this apparent ubiquity obtains is fast diminishing, as in 
the cases already mentioned, in those of Cyprea exanthema, Cer- 
vina and Cervinetta, &c. A large proportion of the shells inhab- 
iting the eastern and western shores of the Atlantic, have been 
regarded as identical; and many of them are really so. But the 
closer the comparison, the more it tends to diminish rather than 
increase the identical species. 'The same is found true in rege 
to other classes of animals. In fact the doctrine of the local lim- 
itation of animals, even now, meets with so few apparent excep- 
tions, that we admit it as an axiom in zoology, that species 
strongly resembling each other, derived from widely diverse 
localities, especially if a continent intervenes, and if no known 
or plausible means of communication can be assigned, should be 
assumed as different, until their identity can be proved.* Much 
study of living specimens must be had before the apparent excep- 
tions can be brought under the rule.”—p. x. 
tas a 
may unconsciously mislead others, by their habit of label- 
t C y 6 Miocene ven 
ifferent province, use it s generally wih ©’ 
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