908 PROCEEDINGS OF THE NATIONAL MUSEUM. 



plate wide, nearly straight, set with strong, irregular, taxodont teeth 

 throughout its length; beak cavities moderate, with a row of dorsal 

 scars running obliquely downward and forward; anterior and posterior 

 muscle scars well defined. 



Animal with the palpi semilunar, united to the mantle by a straight 

 border, longer than wide; outer gills generally larger than the inner, 

 united their whole length to the mantle; inner united to the abdominal 

 sac ; genitalia occupying each side the lateral part of the visceral mass as 

 far forward as the foot; mantle closed below the branchial siphon, and 

 united into branchial and anal siphons; anal opening rather small; 

 branchial openinglarge, the two separated by a solid bridge which solders 

 together the extremities of the four branchiai; both orifices have a 

 thickened inner edge, the branchial being furnished with short tubercles 

 or granules; mantle united below posteriorly one-fourth its length; 

 foot large and strong; adductor muscles strong (Pelseiieer). 



Snbgenus PLEIODON Conrad. 

 Characters as in the genus. 



t PLEIODON OVATUS Swainson. 



* Iridina ovata SWAINSON, Phil. Mag., LXI, 1823, p. 112. " OKEN, Isis, 1834, p. 



458.* REEVE, Couch. Syst., 1, 1841, p. 122. pi. xcm. *HANLEY, Biv. Shells, 

 1843, p. 225. * CATLOW and REEVE, Conch. Nom., 1845, p. 68; * Elements of 

 Conch., II, 1860, pi. xxxin, fig. 184. *CLESSIN, Conch. Cab. Ano., 1875, p. 

 230, pi. LXX, fig. 2; LXXI, fig. 2. 



* Platiris (Iridina) ovata LEA, Syn., 1838, p. 33; 1852, p. 54; 1870, p. 88. 



* Pleiodon ovata CONRAD, JL Ac. Nat. Sci. Phila., VII, 1854, p. 298; * H. and A. 



ADAMS, Gen. Rec. Moll., II, 1857, p. 506. 



* PJeiodon oratns CHKNU, Man., 1859, II, p. 148, fig. 728. *SOWERBY, Conch. 



Icon., XVI, 1866, pi. I, fig. 1. -*PjETEL, Conch. Sain., Ill, 1890, p. 188. 

 Iridina exotica CHILDREN, Brando's Jl., XV, 1823, p. ? 

 * Pleiodon macmurtriei CONRAD, .11. Ac. Nat. Sci. Phila., VII, 1834, p. 13, pi. xni; 



VII, 1854, p. 298. 



* Mary aril a (Pleiodon) macmurtriei LEA, Syn., 1836, p. 55. 



* Iridina raleus JAY, Cat., 1850, p. 70.' 



*Mutela raletts H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 506. * P^F/TEL, Conch. 

 Sam., Ill, 1890, p. 187. 



* Platiris (Iridina) lean LEA, Syn. ,1852, p. 54; 1870, p. 88.* 



* Pleiodon leaii H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 506. 'P^TEL, 



Conch. Sam., Ill, 1890, p. 188. 



* Pleiodon splendens CONRAD, Jl. Ac. Nat. Sci. Phila., VII, 1854, p. 299. 



* Iridina splendida CHENU, 111. Conch., 1858, pi. i, figs. 2, 2, 2b, 2c, 2d. 



West Africa. 



The following are unfigured species of Pleiodon : 



* Pleiodon diolibanus BoURGUiGNAT, Moll. Egypt and Ab., 1879, p. 47. 



* Pleiodon elonfjatus BOURGUIGNAT, Moll. Egypt and Ab., 1879, p. 47. Senegal River. 



1 Said to be of Parreyss. 



2 Presented to Dr. Lea by Sowerby as Iridina leaii. Lea believes it to be a yonng. 

 ovatus. 



