1286 DiPi.onoN 



rays. Recently the t}pe came to light and on carefully washing- 

 it the anterior half of the shell is seen to be bottle-green and 

 the hinder half almost black and there are indications of a 

 few, faint rays at the median part of the shell. This and the 

 smaller, less split-up pseudocardinals lead me to believe that 

 it may be distinct. 



Section PjULLOideus Simpson, 1900. 



Bulloideus SI^[PSO^■, Syn., 1900, p. 887. 



Shell rounded, inflated, thin, nearly equilateral, truncate be- 

 hind and slightly so before, with a rather sharp posterior ridge 

 and a dorsal wing; beaks full, rather high, regularly radial; 

 epidermis smooth, bronzy-olive ; pseudocardinals compressed, 

 much elongated, disposed to be split into denticles, two in the 

 right valve and one in the left ; laterals two in the left valve 

 and one in the right ; dorsal scars few and scattered in the 

 rather shallow cavities ; nacre bluish. 



Type, Unio hulloides Lea. 



D[PI,ODON BULLOIDES Lca. 



Shell short elliptical, almost squarely truncate behind, thin, 

 nearly equilateral ; post-dorsal line straight, meeting the trun- 

 cation behind nearly at a right angle ; beaks full but not great- 

 ly elevated ; posterior ridge well-developed, subangular ; pos- 

 terior slope excavated and wrinkled ; surface strongly, uneven- 

 ly, concentrically sculptured, with traces of radial sculpture ; 

 epidermis yellowish-green, bronzy ; left valve with one pseudo- 

 cardinal and two laterals ; right valve with two pseudocardi- 

 nals, the upper smaller, and one lateral, all the teeth lamellar ; 

 muscle scars shallow ; nacre bluish-white, rather dull. 



Length .17, height 40, diam. 27 mm. 



Rio de la Plata. 

 Unio biilloides Lea, Pr. Ac. N. Sci. Phila., IH, 1859, p. 187 ; 



Tl. Ac. N. Sci. Phila., IV, i860, p. 264, pi. xui, fig. 144; 



bbs., VII, i860, p. 82, pi. XUI, fig. 144. — KuSTER, Conch. 



Cab. Unio, 1861. p. 186, pi. Lix, fig. 2. — Sowkrby, Conch. 



Icon., XVI, 1868, pi. Lxxxvni, fig. 275. 

 Margaron (Unio) hidloides Lea, Syn., 1870, p. 55. 

 Diplodon huUoidcs Simpson. Syn., i<>oo, p. 887. 



