220 BRITISH MOLLUSKS. 



shelving finely notched anterior tooth, and a long drawn-out 



posterior one in the right valve interlocking with two pairs of 



similar teeth in the left valve. 

 TJnio tumidus and ovalis, Philippson (1788), Nov. Test. Gen. p. 17. 

 My a ovalis, Pulteney (1799), Cat. Shells, Dorset, p. 27. 

 Mya depressa and ovata, Donovan (1802), Brit. Shells, vol. hi. and iv. 



pi. ex. and exxii. 

 TJnio rostratus, Studer (1820), Kurz. Verz. p. 93. 



My sea ovata and solida, Turton (1822), Conch. Brit. p. 246. pi. xvi. f. 2. 

 TJnio injlatus, Hecart (1833), Mem. Soc. Ayr. Valene. vol. i. p. 145. 

 TJnio Michaudianus, Desmoulins (1833), Act. Soc. Linn. Bord. vol. vi. 



p. 20. 

 TJnio arcuatus, Bouchard- Chantereaux (1838), Moll. Pas-de- Calais, p. 91. 

 Maryaron (TJnio) tumidus, Lea (1852), Synops. Naiad, p. 36. 

 TJnio (Lymnium ) tumidus, Moquin-Tandon (1855), Mist. Moll. vol. ii. 



p. 577. pi. Ii. f. 11 to 14. 

 Sab. Northern and Central Europe. England, chiefly southern and 



eastern parts. (In gently flowing rivers, canals, and ponds.) 

 It will be seen by a comparison of our very characteristic figures 

 of the shells of U. tumidus and pictorum, that the valves in the 

 species under consideration are broader from the umbo to the mar- 

 gin and more wedge-shaped, the umbo being more conspicuously 

 undulately wrinkled. Another peculiarity in the shell of U. tumi- 

 dtis, consists in the epidermis being of a glossy verdigris colour, 

 more or less confluently painted with rays ; and it may be observed 

 that the epidermis is not disposed in such decided equidistant con- 

 centric ridges. The anterior hinge teeth are, it may be added, 

 more elevately developed, and interlock deeper with one another. 

 The animal has much the same colouring in both species, plain 

 white edges to the mantle, except in the vicinity of the branchial 

 orifice, where it is tinged with orange-brown, sometimes a little 

 speckled. The internal nacre of TJ. tumidus is mostly of a delicate 

 silvery-grey colour, but Dr. Gray mentions having received speci- 

 mens collected in a pond in Warwickshire, in which the interior was 

 tinged with salmon-colour. It is seldom that pearls are found in 

 this species, secretion being feeble, and the nacre thin. 



The range of U. tumidus in Britain is limited to England, 

 chiefly the southern and eastern parts, extending in a northerly di- 

 rection to the south of Yorkshire. It is not known in Scotland or 

 Ireland. On the Continent it is a Northern and Central, that is to 

 say, a Germanic, species, not having been collected south of the Alps. 



