1386 MOXOCOXl)Vr..-RA 



Monocondylcea guarayana (I'Orbigny, Guer. Mag., 1835, p. 



38; Voy. Am. Mer., 1843, P- 614, pi. lxviii, figs. 4-5.— H. 



and A. Adams, Gen. Rec. Moll., II, 1857, p. 501; III, pi. 



cxvii, fig. 3.— Chenu, Man., 1859, II, p. 145, fig. 715.— 



Simpson, Syn., 1900, p. 910. 

 Margarita (Monocondylcea) guarayana Le.\, Syn., 1838, p. 28. 

 Unio guarayana Hanijey, Biv. Shells, 1843, p. 213, pi. xxii, 



fig. 14. — SowERBV, Conch. Icon., XVI, 1868, pi. xcvi, fig. 



524- 

 Margaron (Monocondylcea) guarayana Lha, Syn., 1852, p. 45 ; 



1870, p. 7?>- 



This species is somewhat oval in outline, and is distinguished 

 by having two curved, radial depressions in each valve in front 

 of the posterior ridge. 



MONOCONDYI,.13A INERMIS (Spix). 



Shell small, evenly elliptical, rather thin, slightly inequilat- 

 eral ; beaks full and elevated, apparently having a short, deep 

 lunule in front of them ; surface yellowish-green ; nacre pur- 

 plish or pinkish-tinted; hinge line delicate; teeth small and 

 compressed. 



Length 21, height 16.5 mm. 



South Brazil. 

 Aplodon inernic Spix, Test. Fluv. Bras., 1827, p. 32, pi. xxv, 



figs. 1-2. — vox Iherixg, Arch, fiir Nat., 1890, p. 126. pi. 



IX, figs. 1-3. 

 Monocondylcea incrnie Simpson, Syn., 1900, p. 911. 



I have never seen this species and Wagner merely mentions 

 it with a few words of description. The figures, however, 

 are good, probably taken from a young- shell, and show that 

 it is provided with a single, somewhat compressed tooth in 

 each valve. The above measurements are from these figures. 



MoNOCONDYL.E.\ PARCHAPPii d'Orbiguy. 



Shell singularly long rhomboid, compressed to convex, solid, 

 concentically striate, inequilateral ; beaks prominent, rather 

 sharp, turned forward : dorsal outline arched ; anterior end 

 rounded ; base nearly straight ; posterior end obliquely trun- 



