82 POLYGYRATIA. 



A number of forms agreeing with Polygyratia in general characters 

 of the shell are found in Papua and New Ireland. Whether they 

 have actual affinity to the South American types can be decided 

 only by an examination of the soft parts. The excessively peculiar 

 shell argues great antiquity for the group ; and the somewhat similar 

 distribution of Marsupials and Struthious birds suggests the theory 

 of an ancient migration in the case of Polygyratia. Such a theory, 

 however, rests on no known facts of palaeontology or anatomy. 



Subdivisions. 

 Subgenus I. POLYGYRATIA Gray. 



Shell having the whorls rounded at the periphery, the spire flat 

 or concave. South A merican. Three sections, showing slight differ- 

 ences have been named : 



Section Polygyratia. Last whorl provided with an internal barrier 

 of short spiral lamellae ; parietal callus thin, appressed. 



Section Systrophia. Last whorl without internal laminae ; parietal 

 callus thin, appressed. 



Section Entodina. Last whorl without internal laminae ; edge of 

 parietal callus raised, connecting the ends of the lip, and forming a 

 sort of parietal tooth. 



Subgenus II. COXIA Ancey. 



Shell having the whorls flat above, acutely keeled at the shoulder ; 

 spire subconcave, flat, or conical. Papuan region. 



Subgenus I. POLYGYRATIA Gray. 

 Section Polygyratia Gray (restricted). 



Shell solid, typically with opaque dark coloring ; lip expanded, 

 its margin toothless; parietal callus thin, appressed, body-whorl 

 having an internal barrier of short spiral lamellae, on both outer and 

 parietal walls. Type P. polygyrata, pi. 20, figs. 37, 38. 



The internal lamellae are like those of Gorilla. 



P. polygyrata Born, iii, 124. P. quinquelirata Sm., viii, 150. 

 charybdis Morch. P. pollodonta d'Orb., iii, 126. 



