14S 
PINNA. NACRE. 
PINNA. NACRE. 
Shell with two valves, gaping at the larger end 
and fixed at the other by a beard of silky filaments : 
hinge without teeth, the valves being connected by 
the cartilage nearly the whole breadth. 
It may be proper to remark here, that in this family, as 
in all the bivalves, we strictly adhere to our definition of 
the rule of measurement as to the length and breadth; 
that the length should be taken from the hinge to the op¬ 
posite margin, and the breadth from the opposite skits or 
ends. If this rule he admitted with respect to the Solencs, 
some of which are only an inch in length and eight broad, 
no good reason can be assigned why it should not be pre¬ 
served in this genus ; although it has been usual to reverse 
it, and thus bring into confusion a definite and fundamental 
regulation. 
1. Pinna ingens. Great Nacre. 
Pinna laevis. Donovan , pi. 152. 
Shell nearly triangular, dark horn-color, with irregular 
wrinkles running from the hinge to the margin, which often 
break into scaly plates especially towards the broader end, 
and sometimes crossed by a few obscure ridges from the 
broader to the pointed end, which are sometimes more 
distinct and form a few concave spines ; the pointed end a 
little curved, and more or less of a changeable purple or 
green; inside smooth, glossy, pcrlaceous, breaking into 
laminated plates at the pointed end : length at the broader 
end from the cartilage to the margin often seven inches; 
breadth from the pointed to the broad end sometimes 
twelve inches. 
Scotland, Devon, and Cove in Ireland, v. v. 
2. Pinna pectinata. Rough Nacre. Fig. 11. 
Pennant , pi. /2 —Du Costa, pi. 1(5. f. 3—-Dorset Cat. 
pi. 3. f. 3. 
Pinna muricata. Donovan, pi. 10. 
Shell thin, brittle, transparent, light horn-color, triangu¬ 
lar, 
