146 MAZATLAN BIVALVES 
Famity AWVi CUED A: 
Genus PINNA Jun. 
The remarkable similarity in form between the young shells 
of Isognomon and those of this genus, confirms the opinion of 
Dr. W. B. Carpenter (Br. Assoc. Rep. 1833, p. 20,) and, Prof. 
EK. Forbes (Br. Moll. vol. 11. p. 250,) that it ranks in the present 
family. An abundance of large Pinne, sent in the Liverpool 
Col., were unfortunately sold off at once to the keeper of a 
tea garden, where they may be seen built up into the walls, 
and too much disfigured to allow of the species being identi- 
fied. To add to the confusion, an importation of large Pinnze 
from New Guinea having reached Liverpool at the same time, 
were mixed with them, both in the shop, and in the garden 
walls; and some have found their way into collections as 
though from Mazatlan. A similar confusion seems to have 
attended the Pinne sold in London with the Havre Col., on 
some of which the attached Vermetide, corals, &c. clearly 
prove that they came from far distant seas. The three follow- 
ing species are all that can be quoted with certainty as having 
been found in the Mazatlan boxes. Another species, like P. 
maura, but remarkable for its extreme breadth and thickness 
and for the shape of the anterior muscular impression which 
displays a series of ripples, was sent in the 8. W. Mexican 
collection. Some species of this genus alter considerably in 
the shape of the posterior extremity, as they attain maturity. 
The measurements are taken as in Mytilide. 
200. Pinna MauRA, Sow. 
Proc. Zool. Soc. 1835, p. 84.—Hanl. Descr. Cat. p. 255.— 
C. B. Ad. Pan. Shells, p. 250, no. 395. 
Adolescent sheil dark brown, with about 18 rows of irregu- 
lar scales, here and there almost tubular; dark brown; pos- 
terior end produced, margin rather straight, ventral edge 
smooth, slightly inflated ; hinge line incurved near the umbos ; 
anterior impression bilobed. Long. 8°5, lat. 4°5, alt. 1°58. 
Hab.—Panama, in muddy banks, Cuming,—Do., extremely 
rare, C. B. Adams.—Mazatlan ; probably common, as Lieut. 
Belcher (Zool. Journ. vol. iv. p. 362) speaks of the large and 
dangerous shoals of Pinne in the harbour, which cut boats 
with their sharp edges ; L’pool Col. 
Tablet 669 contains one of the very few specimens saved. 
