1 1 o Shell Life 



grey colour, with very thin epidermis, and the beaks 

 nearly central. The animal is pale pinkish, with a 

 long slender foot, and short conical siphon. It is the 

 only native Pisidiuon of an oval form, so it will be 

 readily identified by this feature, and by the almost 

 central position of the beaks. It is generally dis- 

 tributed in pools, ditches, and marshy places. The 

 Shining Pea-shell (P. nitidiim) is nearly round, very 

 glossy and iridescent, pale yellow or pale brown, 

 more strongly grooved than in the other species. 

 The interior is whitish. The animal is also whitish, 

 with a long, finely-pointed foot, and short, funnel- 

 shaped siphon with a notched margin. It is found 

 in lakes and ponds throughout the country. The 

 Rosy Pea-shell (P. milium), though very glossy like 

 the shell of P. nitidum, and grooved in a similar 

 manner, is more nearly oblong than round, and the 

 lower margin is straight instead of curved. * In colour 

 it is yellowish or pale brown, the interior pearly and 

 white. The animal varies in hue from white throuo-h 

 yellow to rosy red, and has a long, slender, some- 

 what conical foot. Like the other species, this is 

 generally distributed throughout the country in still 

 waters. 



All these Orb- shells and Pea-shells are but tiny 

 representatives of the marine Cockles, and, of course, 

 are cockles only by popular courtesy. The Fresh- 

 water Mussels are even more widely separated from 

 their salt-water namesakes, though our native species 

 are not of the insignificant sizes of the Fresh- water 

 Cockles. It has been suggested that all of these 

 fresh-water bivalves have originated in marine, or 

 at least estuarine, species which have become 



