Dr. BE. von Martens on the Subdivisions of Pinna. 85 
gravel, sand, or mud, as is generally known among the fisher- 
men of the Mediterranean, Pinna saccata is attached to the 
sides of rocks or stones, like Mytilus or some species of Arca ; 
this is stated by Rumph, and confirmed by the relative preserva- 
tion of the apices, as well as by the twisted form being repeated 
in some species of Arca and Mytilus. 
In the Pinne integra the limitation of the nacre and the posi- 
tion of the larger adductor muscle is generally at a greater re- 
lative distance from the apices than in the Pinne fisse ; and in 
P. saccata this distance is smallest in proportion to the size of 
the whole valve. 
The fossil Trichites seem to unite the irregular twisted form 
and waved sculpture of Pinna saccata with the size and thick- 
ness of the living P. rugosa, Sow. A specimen of the latter in 
the Berlin Museum, 382 millims. long, has a thickness amount- 
ing to 12 millims., and each valve weighs about 2 lbs. 
The attempt to arrive at a fixed opimion as to the specific value 
of some forms of Pinne known only from single museum specl- 
mens, or from the figures of Reeve, would be an almost hopeless 
task. In the following list, therefore, the several forms which 
have received specific names are placed near each other, as much 
as possible, according to their apparent natural affinity; and 
where the specific value seems to be open to doubt, they are 
connected by —~4. Every one who has had occasion to exa- 
mine a number of individuals of Pinna collected at the same 
locality will have found that there is some amount of variation 
in sculpture and in the general outlines of the shape, indivi- 
dually as well as according to the stages of age; but this seems to 
be greater in some species (for example, P. veaillum, P. nobilis) 
than in others. 
In both the larger sections some subordinate groups may be 
distinguished, according to the prevailing outlines and colouring 
of the whole shell; but these groups are closely connected to 
each other by intermediate species. 
The species marked with an asterisk (*) I have had occasion 
to examine myself with regard to the sinus. 
I. Pinne integre. 
(a.) Of pale colour and rather trapezoidal form. (Pennaria, Mérch.) 
( pectinata, auct. (Linn.?), Reeve, Conchol. Icon. vol. xi. fig. 42; 
pectinata, var. 6, Lam. Encycl. Méth. pl. 200. f.5. P. rudis, 
Poli, Test. utr. Sic. 33.3; Jeffreys, Brit. Conchol. vol. il. 
frontisp. Europe. 
| *truncata, Philippi, Enum. Moll. Sicil. ii. 16.1; Gualt. 79 A; 
Reeve, 35. Mediterranean. 
| ingens, Pennant, Reeve, 53. Britain. 
