NO. 1205. SYNOPSIS OF THE NAIADES— SIMPSON. 913 



* Margaron (Monocondylcea) lentiformis Lea, Syn., 1870, p. 72. 



"^ Aplodon lentiformis voN Ihering, Arch. filr. Nat., 1893, p. 67. — *Nehring, J. 

 de Conch., 1894, p. 82. 



Southern Brazil. 



The following" species is unknown to me : 



" Monocondylcea tamsana Dunker, Mai. Bl., V, 1858, p. 226. 



Genus IHERINGELLA Pilsbry, 1893. 



(Type, Plagiodon isocardioides Lea,) 



Plagiodon Lea, Pr. Ac. N. Sci. Phila., VIII, 1856, p. 79. 

 Iheringella Pilsbry, Nautilus, VII, 1893, p. 30. 



Shell solid, inflated, rounded to rhomboid in outline, with a more or 

 less developed posterior ridge; beaks high, curved inward and forward, 

 without sculpture; epidermis dull olive, cloth-like; hinge teeth imper- 

 fectly developed, nodulous or more or less broken into denticles, there 

 being an irregular tooth in the left valve under the beak, sometimes 

 partially bifid, and two in the right valve, with the pit between them 

 under the beak ; anterior muscle scars deep, i3artially united ; posterior 

 scars shallow ; nacre soft, bluish silvery, iridescent behind. 



Animal unknown. 



(Group of Iheringella isocardioides.) 



Shell rhomboid or isocardia shaped, with a high, distinct, strongly 

 curved posterior ridge; beaks decidedly full and turned forward. 



t IHERINGELLA ISOCARDIOIDES Lea. 



^Plagiodon isocardiodes Lea, Pr. Ac. N. Sci. Phila., VIII, 1856, p. 79.' 



* Plagiodon isocardioides Lea, Obs.,VI, 1857, p. 38, pi. xxxii, fig. 32; * Jl. Ac. N. 



Sci. Phila,, III, 1858, p. 318, pi. xxxii, fig. 32.—* Kuster, Couch. Cab. Unio, 

 1862, p. 292, pi. xcYii, figs. 8-10. 

 ^ Unio isocardioides SowERBY, Conch.. Icon., XVI, 1868, pi. xc, fig. 484. — "P^tel, 

 Conch. Sam., Ill, 1890, p. 156. 



* Margaron {Plagiodon) isocardioides Lea, Syn., 1870, p. 71. 



Eiio de la Plata; Eastern Peru 1 



IHERINGELLA SEMISULCATA H. Adams. 



* Monocondylcea {Plagiodon) semisMZca/a H. Adams, Pr. Zool. Soc. Loncl., 1870, p. 



376, pi. XXVII, fig. 3. 



Eastern Peru. 



(Grroup of Iheringella rotundata.) 

 Shell somewhat rounded, sublenticular, j)osterior ridge rather low. 



t IHERINGELLA ROTUNDATA Mousson. 



"" Plagiodon rotiindatus MoussoN, Mai. BL, XVI, 1869, p. 187.— * Ppeiefer, Nov. 

 Conch., IV, 1876, p. 139, pi. cxxxi, figs. 8, 9. 



South America. 



' Printed as above. A typographical error, probably. 



Proc. N. M. vol. xxii 58 



