DIPLODON 1227 



curved laterals, the lower stronger; right valve with two pseu- 

 docardinals, the vipper compressed, the lower often split, with 

 a deep scar at their bases, with one lateral ; beak cavities shal- 

 low, showing a few, large dorsal pits ; muscle scars irregular ; 

 nacre white, sometimes having a dull purplish tint, thicker in 

 front. 



Length 80. height 50, diam. 30 mm. 



Length 72, height 42, diam. 26 mm. 



Length 83, height 56, diam. ;^^ mm. 



Argentina ; Paraguay ; Uruguay ; Southern Brazil. 

 f Unio delodonta Lamarck, An. sans Vert., VL 1819, p. yy. — 



Delessert, Rec. Coq. Lam., 1841, pi. xii, fig. 7. — Chenu, 



111. Conch., 1858, pi. XII, figs. I, la. 

 Margarita (Unio) delodontus LEu\, Syn.. 1836, p. 26; 1838, 



p. 20. 

 Unio delodontus Hanley, Biv. Shells, 1843, P- ^94^ P^- ^^i, 



fig. 56.-^Kuster, Conch. Cab. Unio, 1861, p. 234, pi. lxxviii, 



% 5- 

 Margaron (Unio) delodontus Lea, Syn., 1852, p. 29; 1870, 



p. 46. 

 Diplodon delodontus Simpson, Syn., 1900, p. 873. 

 Unio deiodon Strobel, Mat. Mai., Pt. i, 1874, p. 71. 

 Unio lacteolus Lea, Tr. Am. Phil. Soc, V, 1834, p. 40, pi. viii, 



fig. 19; Obs., L 1834. p. 152, pi. VIII, fig. 19. 



T am unable to decide what Lamarck's delodontus is from 

 his brief Latin description. Dr. Lea examined Lamarck's 

 shells and suspects that the delodontus equals his lacteolus, 

 but is not sure of it. I think under the circumstances it would 

 be best to use Lea's name, as his species is properly described 

 and figured, while Lamarck's description gives no locality or 

 account of radial beak sculpture. The species is a very varia- 

 ble one and appears to be abundant over a wide region. There 

 is much variation in form, inflation, solidity, color and charac- 

 ter of the pseudocardinals. After carefully comparing Lea's 

 wheatleyanus with a lot of shells recently received from South- 

 ern Brazil I am doubtful whether it should be separated from 

 lacteolus. 



