1242 DIPLODON 



Margarita (Unio) uiodcstiis Lka, Syn., 1836, p. 32; 1838. p. 22. 

 Margaron (Unio) modrstus Lea^ Syn., 1852, p. 33; 1870, p. 54. 

 Unio modestns H. and A. Adams, Gen. Rec. Moll., II, 1857, 



P- 493- 

 Diplodon leai Simpson, Syn., 1900. p. 876. 



It is a small, rather solid, inflated, rhomboid shell, with a 

 brown epidermis, which scarcely shows a tint of green. 



Lea credits this to Ferussac in his Synopsis, but I do not 

 think it has ever been described by that author or anyone else. 

 In 1856 Kuster properly described and figured a species in the 

 Conchylien Cabinet (Vol. Unio, p. 147, pi. xijii, fig. 2) under 

 the name of Unio modesfus, which he credits to Charpentier's 

 manuscript, a different shell from that referred to by Lea and 

 the Adams brothers. If the latter was never described the 

 name niodcstiis can not be used for it, as it was first properly 

 applied to another species. 



DiPi.ODON RHUACoicus (d'Orbiguy ) . 



"Shell elongate-oblong, inflated, thick, smooth or concen- 

 trically rugose ; epidermis greenish-brown ; beaks radially cos- 

 tate ; anterior end short, roimded ; posterior end elongate, obi- 

 tuse, obliquely truncate ; within bluish-White. 



Length 63 mm., compared wdth the length: height 5i/i(X), 

 diam. 43/100, length of posterior margin 67/ too; apical angle 

 145°." (d'Orbigny). 



Uruguay. 

 Unio rhuacoica d'ORBiGNY, Guer. Mag., 1835, p. 35 ; Voy. hn\. 



Men, 1843, P- ^^y pl- LXix, figs. 4, 5. 

 Margaron (Unio) rhuacoicus Lea, Syn., 1870, p. 54. 

 Diplodon rhuacoicus Simpson, Syn., 1900, p. 876. 

 Unio rhyacoicus von Martens, Mai. Bl., XV, 1868, p. 195. 

 Monocondykca rhyacocca P.EThe, Conch. Sam., Ill, 1890, p. 



174. 



"This species is rounded at the ends like U. charrnana, but 

 is to be distinguished by its shape, which is very much more 

 elongated, narrower, with the dorsal and ventral margins par- 

 allel and also more inflated. It is possible, nevertheless, that 

 this species, in spite of these differences found in a good num- 



