84 Trans. Acad. Sci. of St. Louis. 



teeth on the parietal wall and six old peristomes crowded 

 together. The parietal teeth are long, thin and curved, and 

 the whole shell is very much distorted. 



*78a. POLYGYRA MONODON FRATERNA Say. 



*79. PoLYGYRA LEAH Ward. 



Section Triodopsis Rafinesque. 



80. POLYGYRA PALLIATA Say. 



Station 16. Pittsford (Walton); Cayuga (Banks). 



POLYGYRA TRIDENT ATA Say. 



Stations 1, 4, 5, 7, 13 and 17. Rochester (Walton); 

 Cayuga (Banks). This species is very common, especially 

 at Station 1, where it is found attached to the under side of 

 logs and sticks. It is subject to very great variation and 

 several varieties have been made ; whether there are additional 

 varieties or whether those named are worthy of distinction is 

 the question that confronts the student. In the present lot 

 there are the following forms or varieties.* The novelties 

 herein described are apparently fully adult specimens. 



81. P. TRiDENTATA Say. Typical (Plate X. fig. 1). 



This form is characterized by two large peristome teeth and 

 a small, almost straight parietal tooth which is directed 

 between the two peristome teeth. 



81a. P. TRIDENTATA JUXTiGENS Pilsbry. (Plate X. fig. 3.) 



Station 1. Similar to the typical form, but the distance 



between the teeth on the peristome is considerably less and 



the parietal tooth is much larger, is curved and is directed 



toward the upper tooth on the peristome. 



81b. P. TRIDENTATA (Plate X. fig. 4.) 



Station 1. In this form (which is a variety of the above) 

 the teeth on the peristome are very small and are very wide 

 apart ; the tooth on the parietal wall is like the last variety. 



* See Pilsbry, Proc. Phil. Acad. Sci. 1894: 11-21. 



