MUSSEL AND COCKLE. 55 



These Naidm have not a bissus like the Marine Mussels, 

 they are therefore never attached to one object ; they use their 

 foot as a propeller in traversing the muddy floor of the pond 

 or river, and they have a very funny way of getting along 

 indeed; first, they open the valves of the shell, put out the 

 foot, and after some little hard work, manage to set themselves 

 up on edge; they then proceed by a series of jerks, leaving 

 a deepish furrow in the mud behind them. 



We will now go to Fig. 3, the Spined Cytherea, the Cy- 

 tlierea or Venus Dione of naturalists; the meaning of the term 

 is the mother of Venus, who was, as you will remember, the 

 goddess of beauty, given to this shell perhaps because it is 

 entitled to occupy a place at the head of the Chjtherea, a 

 genus of the Cardiidcs, or Cockle ,. family, of which genus there 

 are about seventy-eight living species; this, as it is the most 

 rare, is also, perhaps, the most beautiful; it is found in the 

 seas of America, and is remarkable for the row of spines 

 on the hinder border of each valve; these vary much in size 

 and number, being in some individuals long and far apart, 

 in others, short, thick, and closely set. The colour of the 

 shell also varies considerably, being sometimes of a delicate 

 rose colour; at others, more of a claret; at others again, bor- 

 dering on purple. It was for one of the first discovered 

 specimens of this shell, that £1000 is said to have been given. 

 Truly a Venus of value this; it ought to be called the Queen 

 of Cockles! 



Our next example, (see Fig. 4,) is the Spotted Tridacna, 

 {T. maculatus,) the latter term signifying spotted. In the 

 ChamidcB or Clam family, is placed the Tridacna genus, the 

 discovered species of which are not numerous; they are chiefly 

 found in the Indian seas. The one above mentioned claims 

 pre-eminence for beauty. AVe cannot quite see the applica- 

 bility of the generic name; Tridacyius, in Latin, signifies to 

 be eaten at three bites, but he must be a man of large 

 capacity indeed who could so devour the head of this family, 

 the Giant Tradacna, {T. gigasj a single specimen of which 

 has been known to weigh as much as five hundred and seventy 

 pounds; from three to four hundred is by no means an un- 

 common size. The shell of this giant niollusk is of a very 

 picturesque shape, something like its spotted congener, as we 



