PISIDIUM. 25 



by a local name, when we have at least equally good 

 reasons and authority for adopting a name bestowed by 

 an earlier writer, and which, besides, is not liable to the 

 same objection. This species differs from P. fontinale 

 in its shape being oval instead of triangular, and in its 

 beaks being more central, and blunt or compressed. Its 

 colour is also yellowish- white instead of grey ; and it has 

 much less lustre. It is the Cyclas fontinalis of Nilsson. 



(7. Sound. 

 4. P. NI'TIDUM*, Jenyns. 



P. nitidum, Jen. p. 16, tab. xx. f . 7, 8 ; F. & H. ii. p. 126, pi. xxxvii. f . 14. 



BODY whitish, with sometimes afaint tinge of yellow, caused 

 by the colour of the liver : tube short, funnel-shaped ; orifice 

 wide, and its edges notched or puckered : foot rather long, 

 thin, slender, and finely pointed : mantle bordered with grey. 



SHELL suborbicular, compressed except in the upper part 

 where it is rather ventricose, thin, extremely glossy, iridescent 

 (especially in the young state and near the beaks), finely and 

 regularly striated or ribbed concentrically, with from 3 to 5 

 separate and deeper grooves which encircle the umbonal re- 

 gion, the striae or ribs being rather broad; yellowish-white or 

 light horn-colour : epidermis a mere film : anterior side some- 

 what truncate, but rounded : posterior side slightly produced 

 and sloping abruptly below : lower margin rounded : beaks 

 nearly central, rather prominent, but obtuse : ligament very 

 short, and scarcely discernible : inside whitish, and plainly 

 showing the scars of the adductor muscles and mantle : hinge 

 and teeth as in the two last species. L. 0-15. B. 0-15. 



Var. splendens. Shell of a lemon-colour, nearly half as 

 large again as that of the ordinary form, stronger, less glossy, 

 rather more oblique, and less deeply striated, with the beaks 

 more swollen and the ligament stronger and perceptible. 



HABITAT : Lakes, ponds, and standing water in all 

 parts of the kingdom from Zetland to the Channel 

 Isles. Malm has described and figured it as a Swedish 



* Glossy. 



