PINNA. 



Genus PINXA, Z, 

 Testa aguivalvis, obliqua, longitudinaliter cuneiformis,Jil)ro- 

 laminaris, plerumque sqmmata, umbonibus terminali- 

 bus, laleribus safe hianlibus. Cardo lateralis, eden- 

 tulus, liffamento snbintemo per totam lonyitudinem 

 continuo. Impressio muscularis composita. 

 Shell equivalve, oblique, longitudinally wedge-shaped, fibro- 

 laminar, generally scaled, umboes terminal, sides often 

 gaping. Hinge lateral, toothless, with the ligament 

 rather internal, continued throughout its whole length. 

 Muscular impression compound. 

 The large typical species of this genus, P. rotundala, 

 being an inhabitant of the Mediterranean, it was one of 

 the few shells described by the old Greek father of natural 

 history, Aristotle. His designation of IIiiTa was there- 

 fore adopted by the founder of our nomenclature in his 

 ' Systcma NaturfB ;' aud it is one of the few Linuajan 

 genera that has escaped the knife of modern genus- 

 mongers. The Finnce are so nearly allied in form and tis- 

 sue that they are scarcely susceptible of even subgeneric 

 division. Their chief variation is in sculpture, the scales 

 with which they are mostly armed being in some, as in 

 P. serrata, very minute aud sharp ; in others, as in P. alta 

 and Cumingu, raised and tubulous ; and in others, as 

 in P. nobiUs and rugosa, promiscuously distorted; while 

 many species, as P. fitmata, bicolor, and PhlUppinensis 

 are smooth. They are all of fibrous brittle texture, and 

 often brilliant in colour, though a dull-olive rather pre- 

 dominates. 



The Pinna are chiefly inhabitants of the Old World. 

 Out of fifty species of which the habitats are known, fully 

 half are from the region of the Philippine Islands, Ma- 

 lacca, and the Moluccas. Only one species, abundant 

 chiefly on the south-west coast, inhabits our own shores, 

 and three the Mediterranean and Adriatic. Australia con- 

 tributes six. fine species, aud New Zealand two, Japan one, 



aud the Cape of Good Hope one. Of the western species, 

 comprising only the proportion of a fifth, the three finest 

 are from Panama. Three are from the West Indies, one 

 from Honduras, one from Puerto Portrero, and three from 

 South Carolina. 



In examining the species of this genus, great care is 

 necessary to observe them in different stages of growth. 

 Individuals which in a young state are characterized by a 

 profusion of scales, often become roughly laminated and 

 denuded of sculpture in an advanced stage of growtli ; 

 and the same species is found, even at the same apparent 

 age, so variable as to be scaly in one habitat and smooth 

 in another. All these difl'erences may however be ob- 

 served, and their gradations detected, by sufficiently co- 

 pious observations. 



Species 1. (Fig. a, b, Mus. Cuming.) 



Pinna Chemnitzii. Finn, testa subarcuato-trigond, te- 

 nui, ventricosd, sordide olivaced, longitudinaliter ra- 

 diaiim costatd, costis interdum subobsoktis, miiticis, 

 interstitiis transverse striatic ; concentrice subplicatd, 

 plicis distantibus, cito evanidis ; margine dorsali In- 

 curvato, plerumque muricato-squamato. 



Chemnitz's Pinna. Shell somewhat arcuately trian- 

 gular, thin, ventricose, dull-olive, longitudinally ra- 

 diately ribbed, ribs sometimes obsolete, smooth, with 

 the interstices transversely striated; concentricallv 

 slightly plicated, the folds being distant and soou 

 disappearing; dorsal margin incurved, generally 

 prickly scaled. 



H.4.NLEY, Pro. Zool. Soc. 1858, p. 136. 



Hab. Phdippine Islands ; Cuming. 



A thin ventricose shell of a sombre-olive colour, pricklv 



scaled only along the dorsal edge. 



February, 1859. 



