146 unionid^;. 



of a pale yellowish-white colour. The labial palps are 

 ovate. 



Its distribution is similar to, but rather wider than that 

 of the last species, and has been greatly extended through 

 the agency of canals. The Kennet, Avon, Ouse, Aire, 

 Don, and Severn include it among their inhabitants, also 

 the canals about London, Birmingham, and Hull. Staf- 

 fordshire, in Chillington Pool (Jeffreys) ; Shrewsbury 

 Canal, and near Eyton (Eyton) ; Scarborough (Bean). 

 " Mr. Hogg states that it has been found in the ponds at 

 Wynyard, on the authority of Sir \V. C. Trevelyan, Bart. 

 It has not been met with further north." (Alder). 



Generally distributed throughout the less mountainous 

 and plain parts of Europe, from Sweden to Naples. 



U. MARGARITIFERUS, Lilllia3US. 



Solid : epidermis black ; no lateral teeth. 



Plate XXXVIII. as Alasmodonta margaritifera. 



Lister, Hist. Conch, pi. 149, f. 4. 



Mya margaritifera, Linn. Syst. Nat. ed. 10, p. 671 ; ed. 12, p. 1112 ; Fauna 

 Suecica, ed. 2, p. 516. — Pennant, Brit. Zool. ed. 4, vol. iv. 

 p. 80, pi. 43, f. 18. — Da Costa, Brit. Conch, p. 225J 

 pi. 15, f. 3. — Donov. Brit. Shells, vol. iii. pi. 73.— Mont. 

 Test. Brit. pp. 33, 561. — Maton and Back. Linn. Trans, 

 vol. viii. p. 40. — Muller, Verm. Terr, et Fluv. p. 210. 

 —Turt. Conch. Diction, p. 106. f. 47- — Chemn. Conch. 

 Cab. vol. vi. p. 15, pi. 1, f. 5. — Dillw. Ilecent Shells, 

 vol. i. p. 52. — Index Testaceolog. pi. 2, Mya, f. 30. 



Die Perlenmuschel, Schroter, Fliissconch. p. 168, pi. 4, f. 1. 



Unio margaritiferus, Betzius, Nova Genera Test. p. 16. — Turt. Dithyra Brit, 

 p. 242, pi. 16, f. 1 ; Manual L. and F. W. Shells, p. 19, 

 pi. 2, f. 9. — Forbes, Malacol. Monensis, p. 44. — Speng- 

 ler, Shrift. Nat. Selsk. Kiobenh. vol. iii.pt. l,p. 52. — 

 Draparn, Moll. Terr, et Fluv. France, pi. 11, f. 5. — 

 Pfeiffer, Deutsch, Land und S'ussw. Moll. pt. 1, p. 116, 

 pi. 5, f. 11.— Nilsson, Moll. Suecise Terr, et Fluv. p. 103. 



