1296 DIPLODON 



related to the forms of Australia. The other Papuan Union- 

 id?e are evidently most nearly related to species of Southeastern 

 Asia. The ])resence of this true HyridcUa in Papuan waters 

 is another point in favor of the theory of a recent connection 

 of this great island with Australia by way of Torres Straits. 



Dii'LODON viTTATus (Lea). 



•Shell subelliptical or subrhomboid, convex or subintiated, 

 subsolid, inequilateral ; beaks slightly elevated and inflated ; 

 posterior ridge rounded or feebly double ; surface very finely, 

 concentrically striate ; epidermis yellowish-olive, with dark, 

 narrow rest marks, subshining ; teeth rather delicate ; pseudo- 

 cardinals compressed ; laterals curved ; nacre whitish to dirty 

 purplish, iridescent behind, thickened in front. 



Length 64, height 43, diam. 25 mm. 



Length 56, height 36, diam. 21.5 mm. 



Australia. 

 Unio vittatns Lea, Pr. Ac. N. Sci. Phila., IIL 1859, p. 153; 



Jl. Ac. N. Sci. Phila., IV, i860, p. 249. pi. xxxviii, fig. 128; 



Obs., VII, i860, p. 67. pi. XXXVIII, fig. 128. — Reeve, Conch. 



Icon., XVI, 1864, pi. XXIII, fig. 83. 

 Margaron (Unio) vittatns I<ea, Syn., 1870, p. 35. 

 Diplodon vittatns Simpson\ Syn., 1900, p. 890. 



The type of this shell is not in the Lea collection, but a 

 specimen presented by "Sir. Cuming to Dr. Lea is. It differs 

 considerably from the type, being subrhomboid. somewhat nar- 

 nowed mi front, in having short pseudocardinals and lurid pur- 

 plish nacre, while the type is nearly elliptical, has somewhat 

 elongated pseudocardinals and white nacre. Both agree in the 

 external color, a sort of yellowish-olive with well-defined, dark 

 rest marks and in this character dift'er from anstralis, to which 

 it seems to be closely allied. 



D1PL.ODON i.ESSONi (Kuster). 



Shell oblong, a little narrower in front, inequilateral, sub- 

 inflated ; dorsal outline somewhat arched ; base line nearly 

 •straight : anterior end rounded ; posterior end widely and al- 

 most s()uarely subtruncated ; epidermis nearly black ; surface 



