264 FUNCTIONS AND INSTINCTS. 



nearly related to the cockle, are mostly fossils 

 but there is one recent species, found on the 

 coast of New Holland, called originally, from 

 the pearly lustre of the inside of its shells, the 

 pearl trigon, 1 a name changed, without reason, 

 by Lamarck. This, which was originally taken 

 by Lesueur and since by Capt. King, was more 

 recently brought from thence by Mr. Setchbury, 

 who told me, that they would leap over the 

 gunwhale of a boat in which he was, to the 

 height of above four inches. The foot of this 

 animal is bent at an acute angle, so, as upon 

 pressure, to form a very elastic organ, 2 and that 

 of the cockle is nearly the same. 



Those elegant shells the Pectens, or comb- 

 shells, have long been celebrated for their 

 motions. Pliny says, probably meaning these 

 shells, that they leap and flutter out of the 

 water, and dive. D'Argenville relates, that 

 when they are on shore, they regain the water 

 by opening the valves of their shells as wide 

 as they can and then shutting them briskly, 

 by which they acquire sufficient elasticity to 

 rise three or four inches, and thus proceed till 

 they accomplish their object. Most probably 

 the foot assists in producing these leaps. Their 

 progression in the water is described as very 

 different ; when they rise to the surface but the 



1 T. maryaritacea. 2 PLATE V. FIG. 5. 



