NO. 1205. SYNOPSIS OF THE NAIADES SIMPSON. 913 



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



* Aplodon lentiformis vox IHERING, Arch. fiir. Nat., 1893, p. 67. *NEHRING, J. 



de Conch., 1894, p. 82. 



Southern Brazil. 



The following species is unknown to me : 



41 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, partially 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. 1 



* Plagiodon isocardioides LEA, Obs., VI, 1857, p. 38, pi. xxxn, fig. 32; *J1. Ac. N. 



Sci. Phila., Ill, 1858, p. 318, pi. xxxn, fig. 32. * KUSTER, Conch. Cab. Unio, 

 1862, p. 292, pi. xcvn, 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. 



Eio de la Plata; Eastern Perul 



IHERINGELLA SEMISULCATA H. Adams. 



* Monocondylcva (Plagiodon) semisulcata H. ADAMS, Pr. Zool. Soc. Lond., 1870, p. 



376, pi. xxvn, fig. 3. 



Eastern Peru. 



(Group of Iheringella rotundata.) 

 Shell somewhat rounded, sublenticular, posterior ridge rather low. 



f IHERINGELLA ROTUNDATA Mousson. 



* riagiodon rotundatus MOUSSON, Mai. Bl., XVI, 1869, p. 187. *PFEIFFER, Nov. 



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



South America. 



1 Printed as above. A typographical error, probably. 

 Proc. N. M. vol. xxii 58 



