1226 niPLODON 



Shell elongated, subtrapezoidal, inflated. 



Group of D. parallelipipedon. 

 Beak sculpture of broken, curved bars. 



Beak sculpture strong, irregular, extending over the 



disk. Group of D. dorsnosus. 



Beak sculpture moderate, of small area. 

 Shell covered with pustules. 



Group of D. novcehollandue. 

 Shell scarcely or not at all nodulous. 



Oval to elliptical. (iroup of D. men:;eici. 



Long, rhomboid. Group of sliuttleworthii. 



Subgenus Dipi.odon s. s. 



Beak sculpture consisting of unbroken ridges, covering the 

 whole beaks. 



Animal having the labial palpi rounded below and at pos- 

 terior base, scarcely projecting behind. 



Type, Diplodon eUipticiim Spix. 



■ Group of Diplodon lacteoins. 



Shell elliptical to subtrapezoidal, inflated, subsolid, with a 

 low posterior ridge, sometimes having a slight posterior dor- 

 sal wing ; one or two central pairs of bars of the beak sculp- 

 ture usually joining below; pseudocardinals, sometimes slight- 

 ly dentellate. 



Animal having the characters of the genus. 



Diplodon lactkoi.us (Lea). 



Shell solid, unevenly elliptical or subrhomboid, subinflated, 

 inequilateral, with a full rounded posterior ridge, which ends 

 behind below the median line ; beaks moderately full, raised 

 but little above the dorsal border, sculptured with strong, 

 radial ridges ; surface irregularly sulcate ; epidermis yellow- 

 ish or greenish-brown, sometimes dark brown, dull or slightly 

 shining ; left valve with two subcompressed. but strong, pseu- 

 docardinals. which are often rough and split up. and two 



