410 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
do uot indicate the species with any precision, while those under question 9 have the 
same uncertainty, as the terms employed to designate the shells most prolific in 
pearls are the local and popular names already mentioned under the head of question 5. 
In response to question 10, as to the proportion of shells in which pearls are found, 
the answers vary so much that no general result can he gathered from the estimates. 
This extreme diversity is due in the first place to the fact that no standard meaning 
is attached to the term “pearls,” some of the papers including any such objects found 
in the shells, while others confine the answer to those that have marketable value. 
This, of course, involves very great differences, as the small and irregular pearls are 
somewhat common, while those of good size, form, and luster are, by all accounts, 
very rare. Other differences are due to natural causes, the productiveness in pearls 
varying with different species, different conditions, different streams, and different 
years. 
The estimates given in 78 papers which undertake to answer the inquiry range 
from 1 pearl in 20 to 1 in 100,000 (Iowa). A paper from Michigan and one from Ten- 
nessee give a ratio of 1 in 20 ; five give 1 in 50, nineteen 1 in 100, five 1 in 200, two 1 in 
300, five 1 in 500, ten 1 in 1,000, and so on up to 1,500, 3,000, 6,000, 10,000, etc. Many 
state that the proportion varies in different streams ; thus a Hew York paper says, for 
the main branch of De Grasse River, 1 in 3,000; for the north branch, 1 in 500; and 
for small brooks in the neighborhood, 1 in from 300 to 800. Others refer to differences 
in different species; thus a Tennessee circular gives 1 pearl in 5,000 of the “yellow” 
mussel, 5,000 to 6,000 of the “rock” or “lake” mussel, 8,000 of the “biscuit,” and 10,000 
of the “black”; in other species even scarcer. This is for pearls valued at $25 and 
upward. Others allude to differences in seasons; thus the Maryland paper states 
that 5 bushels of shells yielded 3 pearls in 1888, while none were obtained from 160 
bushels in 1889. Several papers make no attempt at an estimate, and simply state 
that valuable pearls are “scarce” or “very scarce.” 
In the answers to question 11, as to whether the pearl-bearing shells display any 
distinguishing peculiarities of size or form or other features that may indicate the 
presence of pearls within, the same diversity appears, in some respects, that has been 
noted under several of the previous heads, and for the same reason, no doubt, viz, 
differences of locality and of species. Eighty-eight papers make more or less response 
to the inquiry; of these, 17 are undecided or indefinite; 11 state positively that there 
are no criteria; 14 say that pearls occur chiefly in large shells, 32 in medium sized, 
and 8 in small; 3 state that the presence of a large pearl is indicated externally by 
a bulging or protuberance of the shell (Hew York and Tennessee), or by a ridge 
(Tennessee); 8 refer to some peculiarity of form as indicative, but rather vaguely, 
and 2 (Tennessee) observe that the shells appear to have been injured at some time. 
Several refer particularly to old or old-looking shells, and to those of rough aspect or 
moss-grown, while a Hew York paper specifies “the brightest and clearest.” Many 
state that young and small shells contain no pearls of value, .as would naturally be 
expected. Several mention particular kinds as the best, using the local names; but 
these answers belong properly under question 9. 
Question 12, as to the nature and origin of pearls, in the view of those familiar 
with their occurrence in the fresh- water mussels, has brought out a general agree- 
ment among the majority of those who respond, in favor of the usual theory that 
they are due to the presence of some irritating foreign substance. Other views are 
