io8 Shell Life 



The Horny Orb-shell (aS'. corneitvi) is common in 

 most ponds and streams throughout the country. 

 The beaks are placed almost in the centre 

 of the upper margin of this almost globular 

 shell, which is covered- with a thin glossy 

 epidermis. The colour is that of horn with 

 some lighter bands running parallel with 

 the lower margins. The teeth are well developed. 

 The length is about half an inch, and the animal's 

 span of life is about two years. The Nut Orb-shell 

 {S. rivicola) is a much larger, more oval, and more 

 solid-looking shell, and its colour is yellowish brown. 

 It is covered by a thick brown epidermis, and has 

 stronof concentric ribs. The hintre-teeth 

 are similar to those of S. coriieuin, but 

 much stronger. The interior of the shell 

 has a pearly coating. The animal, like 

 S. corneuQii, is greyish, but the broader 

 foot is less pointed, and the shorter siphons are 

 nearly of the same length and whiter. Though not 

 found in stagnant water, it is not partial to rapid 

 streams; but may be sought in the gently flowing 

 rivers, brooks, and canals of England, from north 

 Somerset and Surrey to south Northumberland. The 

 Oval Orb -shell (S. pallichimi) is a local shell of 

 oblong form, much flatter than the foregoing, thin 

 and semi-transparent, with fine concentric grooving. 

 The animal is white, with a long tongue-shaped foot, 

 and the long siphons are connected almost throughout 

 their length. It occurs only in England, and there 

 its range is limited to Surrey, Middlesex, Warwick- 

 shire, Lancashire, and Yorkshire, where it is found 

 in ponds and canals. The last of the quartette, the 



