Plates i— 21 



Specimen numbers preceded by M are Dzibilchaltun archaeological lot numbers; those 

 preceded by Q are Isla Cancun archaeological lot numbers; simple numerals are Tulane 

 University catalogue numbers of inodern specimens. Precise data on stratigraphical associa- 

 tion of archaeological shells and provenience of modern specimens are available at the 

 Middle American Research Institute, Tulane University. 



Archaeological shells are designated by single lowercase letters; modern specimens, by 

 double lowercase letters. 



