32 HAY. [Vol. IV. 



of the basibranchial, the calcific deposit forms a shell surround- 

 ing the rod of cartilage, but the deposit is also invading the 

 cartilage extensively. 



For the opportunity of making my investigations on this 

 extremely interesting animal, I am indebted to Dr. John C. 

 Branner, Director of the Arkansas Geological Survey, and to 

 the liberality of the management of the National Museum. 



