128 THE NAUTILUS. 



cularis Gld., its most prominent characteristic being the nearly 

 plane upper surface with a strong peripheral carina. It resembles 

 umbilicatus in being spirally striate and having a columellar tooth, 

 but differs in the greater development of the carina, narrower umbili- 

 cus and in having the spiral lines much weaker. It differs from 

 tantillus in the greater development of the carina, in the small but 

 round umbilicus, dentate columella and weaker spiral striation. The 

 animal is black. 



All these species of Neoplanorbis were discovered by Mr. Herbert 

 H. Smith in the fall of 1907. They live on the under sides of stones 

 in the more or less rapid current and in suitable localities are very 

 abundant. Mr. Smith took 50 from one small stone. Neoplanorbis 

 seems very local in its distribution. It may be abundant on one 

 shoal and not found at all on another. And on the same shoal, it is 

 frequently restricted to one side of the river or the other. 



In his progress down the river in 1907, Mr. Smith did not find 

 Neoplanorbis at all, until he reached Cedar Island, Chilton Co., 

 three miles above the mouth of the Yellowleaf Creek, where a single 

 specimen of umbilicatus was found. 



At " The Bar " two miles further down umbilicatus was found in 

 some abundance on stones in a strong current, while at the same 

 place carinatus was found in a moderate current. There was no 

 intermingling of the species in these two situations. Umbilicatus 

 was not met with below this point. 



At Butting Ham Shoals, five miles below, in a moderate current, 

 the catch was almost entirely carinatus, the exception being three 

 specimens of smilhii. 



At Higgins' Ferry, seven miles further down stream, in a moderate 

 current, with the exception of a single example of carinatus, the 

 several hundred specimens were all smithii. 



While at Duncan's Riffle seven miles below, the catch contained 

 two specimens of smithii, the balance being carinatus. 



Duncan's Riffle is twenty-four miles by river above Wetumpka, so 

 that, in view of these facts, it is not surprising that N. tantillus was 

 not met with at all. 



The following key may be of assistance in differentiating the four 

 species of Neoplanorbis now known : 



1. Umbilicate, columella dentate 3. 



2. Perforate, columella smooth 4. 



