Ill 



I MO TETRALASMUS. 



Plati LXI. 

 DESCRIPTION. 



Shell oblong, elliptic, rather thin, moderately con- 

 vex; beaks but little elevated, decorticated; hinge 

 margin parallel to the basal margin, subrectilinear; 

 anterior margin regular]) rounded; posterior >\'<\*' 

 with t\*<» compressed lines; posterior margin declin- 

 ing in an oblique rectilinear hue from the extremity 

 ol the hinge margin to the subrostrated tip; basal 

 iiwiri.Mii subrectilinear; umbonial slope n<>t prominent; 

 within white, iridescent posteriorly and on the mar- 

 pin; numerous minute slightly impressed radiating 

 lines; cardinal teeth transverse!) l<»n<:. slender, very 

 oblique; lateral teeth distant from the cardinal teeth, 

 two in each valve, equally prominent in the two 

 valves. 



SYNOXYME 

 I . jiir u A-m «, Say. Amer. Conch., pi. xxiii. 



DESCRIPTION 



I have not seen this species, and have, therefore, 

 copied Say's description in |>art, and am indebted 

 to the great liberalit) of Mr>. Say for the use of the 



plate originally published in the American Con- 



v 



