146 MAZATLAN BIVALVES 



FAMILY AVICULID.E. 

 GENUS PINNA Linn. 



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. 

 E. Forbes (Br. Moll. vol. ii. p. 250,) that it ranks in the present 

 family. An abundance of large Pinnae, 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 Pinnae 

 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 Pinnae sold in London with the Havre Col., on 

 some of which the attached Vermetidae, 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 S> 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 Mytilidae. 



200. PINNA MATTKA, Sow. 



Proc. -Zool. Soc. 1835, p. 84. Hani. Descr. Cat. p. 255. 



C. B. Ad. Pan, Shells, p. 250, no. 395. 



Adolescent shell 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, lot. 4' 5, alt. 1*58. 

 Sab. Panama, in muddy banks, Cuming, Do., extremely 



rare, C. J3. Adams. Mazatlan ; probably common, as Lieut. 



Belcher (Zool. Journ. vol. iv. p. 362) speaks of the large and 



dangerous shoals of Pinnae in the harbour, which cut boats 



with their sharp edges ; L'pool Col. 



Tablet 669 contains one of the very few specimens saved. 



