150 UNIONIDE. 
edulis” (the common sea mussel). This, however, is not 
likely, as the pearls from this shell are exceedingly few and 
poor. ‘Tacitus writes that they were of marine origin. 
Pennant states that as many as sixteen pearls have been 
found in a single Uzio, and he gives an account of pearls 
of value having been found in Donegal and in the Conway. 
The ancient writers agree in disparaging the British 
pearls, justly considering those from the East finer in size 
and quality. 
Tacitus mentions a theory current in his time that the 
dull reddish colour of our pearls was due to their being 
collected from cast-up shells instead of being gathered 
from living shells from the bottom of the sea ; but he adds, 
with characteristic dry humour, that the fault probably lay 
in the pearls themselves, as otherwise his avaricious 
countrymen would have been sure to discover the best 
method of obtaining them. 
I understand that at Waterford this species goes by the 
name of the ‘Sugar loom.’ 
Var. I. stnudta(Zam.). Broader than the type, yellowish; 
lower margin incurved. 
Var. II. roissyt (Mich.). Longer than the type, lower 
margin rounded outwards. 
