The ears of Pccten are equal in some species and une* 

 qual in others, but generally on one of the valves one of, 

 the ears is deeply emarginated beneath, to admit the pas- 

 sage ot the byssus, by which the animal attaches itself to 

 foreign bodies, as represented by Reaumur in Mem. Acad. 

 Iloyale dcs Sc, 1711, pi. 2, fig. 12. Some species have a 

 small divergent tooth on each side of the cardinal fosset in 

 one valve, and corresponding depressions in the opposite 

 valve. In many species are several very small tubercles 

 or teeth, at the base of the emarginated ear extending from 

 near the apex to a point beyond tlie ear. 



Many of the Mollusca are fixed during life to one spot, 

 others glide along with a slow and regular snailliiLc move- 

 ment ; but locomotion in this genus is rapid, and by a suc- 

 cession of springs or leaps. An alternate motion of open- 

 ing and quickly and forceably closing the valves, enables 

 them to rise to the surface, and they sometimes make small 

 leaps above it in ricochet. When left upon tlie beach by 

 the recession of the tide, tliry regain the water by the 

 same action. INIr. Lesson immersed a basket of Pectens 

 in the water of the sea, within about six inches of its rim. 

 The individuals, he says, which fcrmed tlie superior lay- 

 er, constrained in their movements by those that were be- 

 neath, after many fruitless efTorts, succeeded in leaping 

 from their prison. No sooner did they fall upon the Vi :i- 

 tt r. tlinn by striking their valves rapidly together. Vnvv 

 ran or rather skipped a few seconds upon the surface and 

 then sunk to the bottom. In this way all the contents of 

 the basket disappeared within fifteen minutes. Smellie 

 repeats from Pliny that " wlun the sea is eahu, troeps, or 

 little flrcts of Scallops, are often observed swimming <.n 



