BIVALVIA. 99 



It may be further described as being furnished with two cardinal teeth in the left 

 valve, the anterior one is somewhat thin, sharp, and angular, sloping towards the muscle 

 mark on that side, the other one on the posterior side of the umbo is thick, strong, and 

 rugose, with a sharp, linear, lateral tooth, nearly parallel to the dorsal margin, or liga- 

 mental fulcrum : the right valve has one large cardinal tooth divided in the middle, this 

 fits into a depression in the left valve of a corresponding form, and parallel to the margin 

 is an elongated, sharp, and elevated, lateral tooth ; the muscle marks are deeply im- 

 pressed, more especially the anterior one, this is rugose and subquadrangular, and is 

 bipartite or has a smaller one adjoining, more within the shell ; the posterior one, 

 placed at the extreme edge of the ligament, is slightly ovate, with the mantle mark 

 parallel to the margin of the shell, connecting the adductors ; the posterior is obtusely 

 angular, and the shell on that side is somewhat compressed or less tumid than at the 

 anterior : the surface of the shell is roughened by irregular and prominent lines 

 of growth ; on many of the individuals there are the remains of the epidermis, and 

 in most instances the specimens have the ligament entire, with the valves in their 

 natural position. 



Several valves in my Cabinet have specimens of Balanus adhering to them, 

 showing the proximity of the Sea at one time to this Deposit, or perhaps the re- 

 occupation by salt-water of the locality once filled with fresh-water and its inhabitants. 



This species has now an extensive Geographical range, being found in the North 

 of France, and in the fresh-waters of the Island of Sicily ; and Lea, in his ' Observations 

 on the Genus Unio,' vol. i, p. 201, says "the shell found in the Euphrates, near 

 Bagdad, is only a variety of this species," and he records it also as the opinion of the 

 Baron de Ferussac. I have never seen this shell. 



2. Unio tumidus, Retzius. Tab. XI, fig. 13. 



Unio tumidus. Retz. Nova. Gen. Test., p. 17, 1788. 



— — Pfeif. Land und Sussw. Moll., pt. ii, p. 34, pi. 7, figs. 2, 3, and pi. 8, 



figs. 1, 2. 



— — Rossm. Icon. Land und Sussw. Moll., pt. i, p. 117, ph 8, fig. 70; 



pt. iii, p. 27, pi. 14, figs. 262—4; pi. 40, fig. 542; pi. 60, 

 figs. 772—778. 



— — Gray. Man. Land and F. W. Shells, p. 297, pi. 2, fig. 13, 1844. 



— — Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 140, pi. 40, fig. 1, 1849. 

 Mya ovalis. Mont. Test. Brit., p. 34, 1803. 



— depressa. Don. Brit. Shells, vol. iii, t. 101, 1802. 



— ovata. Bon. Brit. Shells, vol. iv, t. 122, 1803. 

 Mysca ovata. Turt. Brit. Biv., p. 246, 1822. 



— — Swains. Malac, p. 277, fig. 56, 1840. 



— solida. Turt. Brit. Biv., p. 246, pi. 16, fig. 2, 1822. 

 Unio pictorum. Brown. Ulust. Brit. Conch., pi. 26, fig. 2, 1827. 



— ovalis. Sowerby. Genera of Shells, No. 16, Unio, fig. 1. 



— — Brown. Ulust. Brit. Conch., 2d ed., pi. 31, figs. 1 — 4. 



— rostrata? Desk. 2d ed. Lam., p. 540, t. vi, 1835. 



