MUSSELS. 191 



front of the middle of the shell. The teeth are like those of 

 the last species, but are very small. The muscular scars are 

 indistinct. The shell is about ^in- long, Jin. high, and fin. 

 thick. 



Sphserium corneum is very much commoner than the last 

 species, being found in the rivers, streams, canals, ditches, 

 and ponds of nearly every part of Britain. The body is 

 greyish, and the foot is rather pointed and whitish. The 

 siphons are long, and of a pale flesh-colour. The shell is 

 rather orbicular, and of a light horn-colour. The umbones 

 are central, and the ligament is inconspicuous and short. The 

 teeth are like those of ihe last species, and the muscular 

 scars are indistinct. The shell is about -^^ia. long, ^^in. . 

 high, and -^in. thick. 



Sphserium lacustre (Fig. 126j _ 



is an interesting little bivalve, " - - 



and will live very well in ^^*^^ ^ '^. if^ 



confinement. It is rather a " %~.i^=di«^^^^ 



busy " thread-spinner," and is - - — - ^^ 



found in the running and cssJ^^^S^ 



stagnant water of many parts ■ o*****"*'*^ 



of Britain, but it is rare in „,„ .„, „ 



' - FIG. 126. SPH.ERinM LACUSTHE. 



Scotland. The body is almost 

 white, and sometimes of a 



pale flesh-colour. The siphons are white and long, and the 

 foot is very large for the size of the animal. The shell is 

 nearly round, and of a pale horn-colour. The umbones are 

 prominent, central, and show the first growth of the shell. 

 The teeth are like those of the last species, but are very 

 small. The ligament is inconspicuous, and the scars are 

 indistinct. 



In many respects the Pisidia are very like the SphsBria, but 

 they differ principally in having one siphon instead of two ; 

 they are also niore abundant, and are divided into five species : 

 it is rather difficult, unfortunately, to teU one species from 

 another. Dr. Gwynn Jeffreys says, concerning them, that 

 " size, substance, sculpture, and lustre, are not of much 

 account, as they mainly depend on the chemical ingredients 



