THE NAUTILUS. 



VOL. XI. MARCH, 1898. No. 11. 



MOLLUSCA CONTEMPORANEOUS WITH THE MASTODON. 



BY BRYANT WALKER. 



In THE NAUTILUS for March, 1891, (Vol. VI, p. 131) there is 

 given a list of half a dozen species of fresh-water shells which were 

 found associated with the remains of a mastodon discovered in 

 Randolph County, Indiana. Through the courtesy of Mr. W. Hilles 

 Smith of Niles, Michigan, I have recently had an opportunity of 

 examining a quantity of material taken from the muck beneath the 

 remains of a mastodon found near that city. 



As the list of species is a considerable one it is of interest not only 

 because of the circumstances, under which they were found, but also 

 as a basis for comparison with similar finds from other localities. 



As has been stated by others in reference to the mollusca formed 

 fossil in the loess there is here, in most instances, little, if any, varia- 

 tion from the usual form of the species as they are found living at 

 the present time. 



The Planorbis companulatus Say and bicarinatus Say are both 

 larger than the average size of the species as usually found. In the 

 latter species there is a decided tendency towards a whorl narrow in 

 proportion to its height, with a strong carina on both sides, result- 

 ing in a long narrow aperture in mature examples. 



One of the most abundant species in the collection was Valvata tri- 

 carinata Say, which afforded some unusual forms. As is well known, 

 this species is extremely variable in its sculpture, ranging though 

 the bicarinate and unicarinate forms to that which is ecarinate. In 

 this, however, all the specimens are strongly tricarinate and the 

 variation is in the other direction and in the form of additional car- 

 inoe. This, in one instance, appears as a fourth cariua on the body 

 whorl about half way between the superior and peripheral carinse 

 in the normal shell. In another specimen, a fourth carina is sud- 



