46 Quarterly Journal of Conchology. 



made by piercing a hole through the valves and stringing them upon 

 a wUlow, or similar twig. 



The animal of the fan-shells is exceedingly beantiful. The 

 mantle, or thin outer edge, which is the part nearest the rim or edge 

 of the valves, conforms to the internal fluted stmcture of the latter, 

 and presents the appearance of a delicately pointed ruffle or frUl. 

 This mantle is a thin and almost transparent membrane, adorned with a 

 delicate fringe of slender, thread-like processes or filaments, and 

 furnished with glands which secrete a coloring matter of the same 

 tint as the shell ; the valves increase in size, in harmony with the 

 . growth of the . soft parts, by the deposition around and upon toe 

 edges of membranous matter, from the fringed edge of the mantle 

 which secretes it. This cover is also adorned with a row of conspi- 

 cuous round black eyes {ocelli) aroiind its base. The lungs or gills 

 are between the two folds of the mantle, composed of fibres pointing 

 outward, of delicate form, and free at their outer edges, so as to 

 float loosely in the water. The mouth is placed between the two 

 inmost gills, where they imite ; it is a simple orifice, destitute 

 of teeth, but with four membranous lips on each side of the 

 aperture. 



The pectens have also a foot, less developed than in some others 

 of the bi-valve mollusks, which resembles a crooked finger, and is 

 capable of enlargement and contraction, and assists the animal in 

 moving about on the bottom of the sea. Some of them have a sort 

 of beard (byssus), at least when young, by which they attach them- 

 selves to rocks, seaweeds, and other marine bodies, as do the mussels, 

 which are also bearded ; while others of the scallops live without 

 attach;nient, and move through the water with considerable celerity, 

 with a jerking motion, caused by the rapid opening and closing of the 

 two valves, producing a recoil which carries them along sideways. 

 The young shells of some species dart with great rapidity, a single 

 jerk carrying them several yards. The writer has frequently watched 

 the Atlantic species (P. irradians), and when taken from the water, 

 and as long as life continues, the animal will open the valves and 

 shut them with a snap, the operation pi'oducing a short, sharp, jjer- 

 cussive soimd. 



The mechanism by which respiration and nuti'ition are seciu'ed 

 is elaborate and exceedingly interesting. The filaments of the gUl- 

 fringe, when examined under a powerful microscope, are seen to be 

 covered with numberless minute, hair-like processes, endowed with 

 the power of rapid motion, These are called cilia, and, when the 



