J302 1)1 IM, Olio N 



the posterior, rounded ; dorsal and ventral lines nearly straight 

 and parallel ; dorsal slope slightly and obliquely subtruncate ; 

 surface covered with fine, irregular, concentric sculpture, often 

 slightly corrugated or subnodulous on the disk ; epidermis in 

 young shells clouded, greenish, yellowish and brownish, dark- 

 er in old shells; pseudocardinals small, subcompressed in 

 young shells, becoming stumpy and often faint in old shells ; 

 laterals lamellar ; nacre bluish, iridescent and thin behind, 

 thick in front ; dorsal scars few, distinct. 



Length 61.5, height 28, diam. 12.5 mm. 



Length 58, height 3r.5, diam. 14.5 mm. 



New Zealand, common according to Gould. 

 Unio lutulentus Goui.d, Pr. Bost. Soc. N. Hist., IH, 1850, j). 



295; U. S. Expl. Exp., XII, 1852, p. 428, figs. 542, 542a, 



542&, 542c — Rekvk, Conch. Icon., XVI, 1865, pi. xxv, fig. 



122. 

 Margaron (Unio) lutulentus Lka, Syn.. 1852, p. 32; 1870, p. 



52. 

 Diplodon lutulentus Simpson, Syn., i<X)0, p. 892. 



A puzzling form, which in some cases approaches danger- 

 ously close to forms of menziezi. There are three valves in 

 the National Museum collection marked "Type," which do not 

 agree very closely with the figures in Gould's Atlas. The 

 figures show a rather brightly colored shell, while these valves 

 are dull and, as is often the case with this species, coated with 

 a deposit of oxide of iron. The description tallies well with 

 other shells in the N^ational Museum collection collected by 

 the Wilkes' Exploring Expedition. In general the species is 

 more elongated than any of the forms of inencie::!, more solid, 

 has shorter pseudocardinals, which become stumpy and faint 

 with age. The nacre is more strongly and suddenly thickened 

 in front in this shell. 



DiPi.ODON wiLSONij (Lea). 



Shell oblong, elliptical, convex, inequilateral, thin ; beaks 

 rather full, sharp; posterior ridge low, rounded; dorsal and 

 basal outlines very slightly curved, nearly parallel ; anterior 

 and posterior ends rounded, the latter. a little produced on or 



