102 MOLLUSCA FROM THE CRAG. 
These animals are bisexual, and the young shell is completely formed before 
exclusion, although differing then materially in shape from that of its parent. Their 
power of multiplication is said to be enormous. Mr, Lea states that he counted not 
less than six hundred thousand young in an adult specimen. 
The shells of this genus are also exceedingly variable, more especially in the out- 
ward form; some species have the hinge area largely elevated into the form of a wing, 
and in consequence of these variations, as well as from differences in size of dental 
characters, they have also been separated into several genera. 
It appears to be a modern genus, and only yet known in the fossil state from the 
newer Tertiaries. 
1. ANODONTA CYGNEA, Linneus. Tab. XI, fig. 11. 
Myrinus cyennus. Linn. Syst. Nat., ed. 12, No. 257, 1158, 1767. 
— — Mat. and Rack. Linn. Trans., vol. viii, pl. 3A, fig. 2, 1807. 
— — Poli. Test. Sicil., vol. ii, p. 212, pl. 33, fig. 2, 1795. 
— — Sheppard. Trans. Linn. Soc., vol. xiii, p. 84, pl. 5, fig. 3, 1822. 
—  anainus. Linn. Syst. Nat., ed. 12, p. 1158. 
— — Poli. Test. Sicil., vol. ii, p. 213, pl. 33, fig. 1, 1795. 
= Avonensis. Moné. Test. Brit., p. 172, 1803. 
— — Mat. and Rack. Linn. Trans., vol. viii, p. 250, pl. 3. 
— acuta. Sheppard. Linn. Trans., vol. xiii, p. 88, pl. 5, fig. 6, 1822. 
STAGNALIS. Sowerby’s Brit. Miscellany, pl. 16. 
— —_ Brown. Uust. Brit. Conch., pl. 27, fig. 2, 1827. 
—  vpenratus. Twurt. Conch. Dict., p. 115, 1819. 
—  mncrassatus. Sheppard. Linn. Trans., vol. xiii, p. 85. pl. 5, fig. 4. 
AnoponTa cyYGNEA. Pfeiff. Land und Sussw. Moll., p. 111, t. vi, fig. 4, 1821. 
— ANATINA, Id. = - - Sie Pye Lb Oe Wtienvils alle an aes 
_ INTERMEDIA. Id. - - - =p: WSS t. vitesse 
ae ventTRIcosa. Kickx. Moll. Brab. Aust., p. 80. 
— prsctnatts. Nils. Moll. Succ. Ter. et Fluv., p. 116, fide Ford. and Hanl. 
— CYGNEA. Rossm. Icon. Land and Sussw. Moll., pp. 1, 111, t. 3, fig. 67, 1835. 
ANODON PALUDOosA. Turt. Brit. Biv., p. 240, pl. 15, fig. 6, 1822. 
Sympuynota cyenea. Lea. Obs. on the Gen. Unto, vol. i, p. 70, 1852. 
Spec. Char. Testa oblongo-ovata, sepe compressa, tenur, interdum tumida et inerassata ; 
anticé rotundatd, postice productd, et angulatd ; natibus depressiusculis, rugosis. 
Shell oblongo-ovate, generally compressed and thin, sometimes tumid or inflated, 
occasionally thick ; anterior side rounded, posterior produced, and angulated ; umbones 
rather flat, with undulating rugosities. 
Length, 33 inches. Hezght, 2 inches. 
Locality. Stutton, Clacton, Grays (Pickering), Cropthorn, and Bacton (A/orris). 
Recent, Britain, and North of Europe. 
This species is abundant in individuals both at Stutton and Clacton, the two 
localities of Fresh-water Deposits that I am best acquainted with, although from 
their great fragility specimens are very difficult to obtain im any degree of 
