• 1
    The internal structure and function of the stomach is described for representatives of seventeen families of Eulamellibranchia.
  • 2
    Detailed comparisons are made among these and comparable data previously obtained from four families in the Filibranchia and Pseudolamellibranchia, and it is concluded that there are no grounds for sub-dividing these twenty-one families into two or more groups. In all cases the stomach is of Type IV.
  • 3
    A new definition for Stomach Type IV is provided.
  • 4
    It is concluded that on the basis of the internal structure of the stomach these twenty-one families appear to comprise a natural and monophyletic assemblage.