97 



The Nautilus. 



Vol. XIII. JANUARY, 1900. No. 9. 



CHANGES WITH GROWTH OF LITHASIA OBOVATA SAY . 



BY BRYANT WALKER. 



Having lately received from Mr. A. C. Billups, of Lawrenceburg, 

 Ind., a package of unsorted material from the Falls of the Ohio, I 

 have been able to trace out the various stages in the growth of this 

 species, which are quite peculiar, ami, I believe, have not been de- 

 scribed. 



The difference in shape between the mature shell and the young is 

 very striking. In the adult, the very large, almost shouldered body, 

 and long, narrow aperture, nearly twice as long as the short, rapidly 

 acuminating and generally eroded spire, is characteristic, of the 

 species, and was well described by Say in his original description 

 published in 1829; while the young shell, until it attains the sixth 

 whorl, is almost spindle-shaped, and would be taken at first glance 

 for a young Goniobasis ; the spire is sharply conical, and longer 

 than the aperture, which is broadly triangular, the long (columellar) 

 side of the triangle being slightly concave. 



The manner in which this remarkable change in shape is brought 

 about is as follows : 



The first two whorls are smooth ami well rounded, and the apex 

 rather obtuse. At about the beginning of the third whorl, a sharp 

 carina is developed on the periphery of the body whorl, which rapidly 

 increases in strength for the next four whorl-. During this stage the 



