117 
PRODUCTA hemisphaerica. 
TAB. DLXI. 
This plate represents some large specimens that were 
formerly referred to P. scotica : but upon an exact com- 
parison, we find they do not agree with the figure in 
Mineral Conchology, tab. 69. f. 3 ; but that in fact half 
of the small specimen drawn at fig. 2. of the present 
plate was given upon tab. 32 8. to show a section of P. he- 
misphaerica ; to which species we see no reason why the 
large specimens should not be referred : and we consider 
the figures of them essential to illustrate it. The very 
narrow space between the valves is a useful character ; 
the total want of spines distinguishes it from P. scotica. 
It is more difficult to distinguish from P. personata 
(tab. 321.), which is perhaps the internal cast of the same 
species, but seems rather more globose. 
We have recently discovered, by purchasing the spe- 
cimen it is taken from, that fig. 11. of tab. 12. of Par- 
kinson’s Organic Remains, which is called Trigonia 
rugosa (vol. iii. p. 177.), is taken from a large crushed 
individual of Producta scabricula (tab. 69. f. 1.). 
