I 196 TirrRAIT.ODON 



Length 60, height 42, diam. 42 mm. 

 Length 48, height 40, diam. 38 mm. 

 Amazon and Rio de la Plata River systems. 

 ? Prisodon truncatus Schumacker, Ess. Nouv. Syst, 1817, 



P- 139- 

 f Castalia ambigua Lamarck, An. sans Vert., VI, 1819, p. 67. 

 — GuERiN, Icon. Regne. An., 1829, pi. xxviii. — Wyatt, 

 Man. Conch., 1838, p. 65, pi. xi, fig. 5. — Chenu, Man., 1859, 



11. p. 149' fig- 735- 

 Unio ambigua Deshayes, Tr. Elem. Conch., 1839, p. 18, pi. 



XXIX, figs. 7-9. 

 Unio ambiguus Sowerby, Rec. and Fos. Shells, XVI, 1823, 



fig. d. — Reeve, Conch. Syst., 1841, p. 117, pi. i^xxvii, fig. 2. — 



Desiiayes, Tr. Elem., II, 1853, p. 219, pi. xxix, figs. 7-9. 

 Tetraplodon ambiguus Simpson, Syn., 1900, p. 863. — von 



Iherinc, Abhandl. Senckenb. Naturt. Ges., 32, 1910, p. 125, 



pi. 12, figs. 4.a-d. 

 Tetraplodon pcctinatum Spix, Test. Fluv. Bras., 1827, p. 32, pi. 



XXV, fig. 3. 

 Castalia inftata d'ORBiCNY, Guer. Mag., 1835, p. 43. — HanlEy, 



Biv. Shells, 1843, P- i73> P^- xxiv, fig. 12. — d'ORBiGNY, Voy. 



Am. Mer. 1843, P- 59^, pl- r.xxii, figs. 4-10. 

 Castalia tnrgida HuPE, Moll. Nouv., Ill, 1857, p. 76, pl. xiv, 



fig. I. — Sowerby, Conch. Icon., XVII. 1869, pl. iii, fig. 11. 

 Castalia haulcyana Sowerby, Conch. Icon., XVII, 1869, pl. i, 



fig- 5- 

 Castalia carolincnsis Sowerby, Conch. Icon., X\^II, 1869, pl. 11, 



i\g. 6. 

 Castalia cordata Strobee, Mat. Mai., Pt. I. 1874, p. 75. 



An exceedingly variable form, some specimens being quite 

 elongated and straight on the base line ; others are much 

 slighter, are rounded below, and almost rhomboid. 



Schumacher gave only a brief description of his Prisodon 

 truncatus, and referred to no figure, and the same can be said 

 of Lamarck regarding his Castalia ambigua, both of which are 

 supposed by authors to be the above species. But either of 

 these descriptions apply equally well to several species, there- 

 fore they can not be considered authentic. 



