UNIO 603 
nals and two short laterals, with a vestige of a third above 
them; dorsal scars numerous, placed in a long row under the 
pseudocardinals; beak cavities not deep; muscle scars large, 
deep; pallial line deep, crenate; nacre silvery, salmon, light or 
deep purple, thicker in front, obliquely ridged and grooved. 
Length 131, height 88, diam. 32 mm. 
Length 135, height go, diam. 33 mm. 
Length 121, height 77, diam. 28 mm. 
Mexico; Central America. 
Unio discus Lea, Tr. Am. Phil. Soc., VI, 1838, p. 74, pl. xvi, 
fig. 57; Obs. II, 1838, p. 74, pl. xvi, fig. 57—HAnNLey, 
3iv. Shells, 1843, p. 197, pl. xxu, fig. 12—Cuenu, II. 
Conch., 1858, pl. xix, figs. 6, 6a, 6b—Stmpson, Syn., 1900, 
Pp. 705. 
Margaron (Unio) discus Lea, Syn., 1852, p. 31; 1870, p. 50. 
Lampsilis discus Pitsery, Pr. Ac. Nat. Sci. Phila., 1909, p. 533- 
Umio discus var. connectans von Martens, Biol. Cent. Amer., 
Moll., 1900, p. 510. 
Unio panucoensis VoN DEM BuscH in Philippi, Abbild. und 
Besch., I, 1843, p. 75. pl. u.-—Kuster, Conch. Cab. Unio, 
1861, pl. LXxxt, fig. 1. 
Unio discus var. panucoensis VON Martens, Biol. Cent. Amer., 
Moll., 1900. p. 510, pl. xxxu1, figs. 2, 2b. 
Unio mexicanus Sowerby, Conch. Icon., XVI, 1867, pl. Lv, 
fig. 281. 
Unio lapidosus KovELt, Nach. Deuts. Mal. Ges., 1893, p. 151; 
Jcon., new ed., VI, 1893. p. 90, pl. cLxxvt, fig. 1120.—Simp- 
son, Syn., 1900, p. 700.—von Martens, Biol. Cent. Amer., 
Moll., 1900, pp. 511, 651. 
A magnificent, ponderous species, which does not seem to be 
very nearly related to anything else, though it has many of 
the characters of the gibbosus group. von Martens in the 
Biologia Centrali Americana, Mollusca, Supplement, page 651, 
states that he has examined the type of Unio lapidosus in the 
Berlin Museum said to come from the Euphrates River, and 
that he feels sure that it belongs to this species. The figure 
of the teeth and muscle scars and a part of the description of 
