402 MOLLUSCA. 



pointed ears, and a more oblique shell. The vestige of a tooth, of 

 which traces are visible in the Pintadinae, is observed on the hinge, 

 before the ligament. 



One species, Mytilus hirundo, L., Chemn., VIII, Ixxxi, 722 

 728, that inhabits the Mediterranean, is remarkable for the 

 pointed ears which extend its hinge on each side. Its byssus is 

 coarse and stout, resembling a little tree(l). 



Pinna, Lin. 



The Pinnse have two equal valves, forming a segment of a circle, 

 or resembling a half-opened fan, which are closely united by a liga- 

 ment along one of their sides. The animal, the Chimjera, Poli, is 

 elongated, like its shell; the lips, branchiae, and other parts are in 

 the same proportion. The mantle is closed along the side of the liga- 

 ment; the foot resembles a little conical tongue excavated by a sul- 

 cus; it is furnished with a small transverse muscle situated at the 

 acute angle formed by the valves, near which is the mouth, and with 

 a very large one in their broader portion. By the side of the anus, 

 which is behind this large muscle, is a conical appendage, peculiar 

 to the genus, susceptible of expansion and elongation, the use of 

 which is unknown(2). 



The byssus of several species of Pinna is as fine and brilliant as 

 silk, and is employed in fabricating the most precious stuffs. Such 

 is the 



P. nobilis, L., Chemn. VIII, Ixxxix; which is moreover re- 

 cognized by the valves being roughened with recurved and semi- 

 tabular plates. It remains half buried in the sand, and anchored 

 by its byssus(3). In the 



Arca, Lin.(4) 



The valves are equal and transverse, that is to say, the hinge occu- 

 pies the longest side. It is furnished with a large number of small 

 teeth, which interlock with each other, and, as in the subsequent ge- 

 nera, with two fasciculi of transverse and nearly equal muscles, in- 



(1) Several species are now made of it. See Lam., An. sans Verteb., VI, 

 part I, p. 146, et seq. 



(2) M. Poli calls it also an abdominal trachea, just as erroneously as he applies 

 the same name to the foot of the Pedines, &c. 



(3) The whole genus Pinna may remain as it is in Gmelin: it is well to remem- 

 ber, however, that some of his species may be found to form but one. See also 

 Lam., An. sans Vert., VI, part I, p. 130, et seq., and Sowerb., Gen. of Shells, 

 No, XXVI. 



(4) M. de Blainville forms his family of the Akcacea or Poltodoktes, from the 

 genus Arca. 



