516 S. WELLER MISSISSIPPIAN RHYNCHONELLIFORM SHELLS 



shell is present; but in its external features the shell is so like R. per- 

 sintiata that the two species can scarcely be distinguished. A series of 

 cross-sections showing the internal features of the species is reproduced 

 in figure 18, and these show the characteristic undivided hinge-plate of 



o o 



^ 8. ». <f& 



Figure 18. — Cross-sections of the rostral Portion of Rhynchopora ? cooperensis 



(Bhumard) 



This series of eight cross-sections is from a specimen from the Chouteau limestone of 



Missouri 



Rhynchopora. Under these circumstances it seems to be safe to refer the 

 species to that genus, although until the punctate shell structure has 

 been observed the reference may be made with a query. 



