MONOCONDYL.;]- A I ogy 



cate; epidermis brownish-green; nacre bluish to rose-color; 

 tooth of the left valve conical, rounded, that of the right low' 

 Length 47, height 28, diam. 19 mm. 

 Argentina. 

 Monocondylaa parchappii d'ORBiGNY, Guer. ]\Iag., 1835, p. 38 ; 

 Voy. Am. Mer., 1843. P- 615, pi. i.xviii, figs. 1-3.— Simpson,' 

 Syn., 1900, p. 911. 

 ^ Margarita (Monocondylcea) parchappii Lea. Svn., 1838, p. 28. 

 Unio parchappii Hani.tty, Biv. Shells. 1843, P- 212, \\. xxii 



%• 13- 

 Margaron (Monocondylcea) parchappii hUA, Syn., 1852, p 45- 



1870, p. ys- 

 Monocondylcea pasii Lea, Pr. Ac. N. Sci. Phila., X, 1866 p 

 34: Jl. Ac. N. Sci. Phila., VI. 1868, p. 2ys, pi. xxxvi, fig. 88 J 

 Ob.s., XII, 1869, P- 36, pi. XXXVI, fig. 88.— Clessin, Conch.' 

 Cab. Ano., 1876, p. 251, pi. i^xxix, figs. 6-7. 

 Margaron (Monocondylcea) pazii Lea, Syn., 1870, p. y^,. 



Decidedly rhomboid in outline and much more compressed 

 than guarayana. Besides, it lacks the radial furrows of that 

 species. 



M0NOCONDY1..EA TABAGUAYANA d'Orbigny. 



Shell subquadrate or subrhomboid. solid, inflated, inequi- 

 lateral, concentrically striate ; beaks full and high ; dorsal line 

 behind them nearly straight; posterior end almost squarely 

 truncate : anterior end rounded, narrowed ; base curved, fullest 

 behind the middle ; above the posterior ridge there seems to be 

 a couple of radial furrows ; epidermis brown-green ; nacre pale 

 greenish, brilliantly iridescent; tooth of the left valve obtuse 

 and nearly triangular. 



Length 59, height 44, diam. 32 mm. 

 Rio de la Plata drainage. 

 Monocondylcea paraguayana d'ORBiGNY, Guer. Mag., 1835, P- 

 37-— SowERBY, Conch. Man., 1839, fig. 149.— d'ORBiGNY, 

 Voy. Am. Men, 1843. P- 612, pi. i^xx, figs. 5-7.— Clessin,' 

 Conch. Cab. Ano., 1876, p. 245, pi. lxxviii, figs, i, 2.— Simp- 

 son, Syn., 1900, p. 911. 



