92 THE NAUTILUS. 



different forms. One specimen, a dead shell, which may be of the 

 same, is high, globose, diam. 25, alt. 21 mill., with the last whorl 

 considerably descending towards the aperture, and the latter quite 

 inferior and oblique, somewhat triangular, like that of P. elevata, but 

 there are only a little over six whorls, and the spire is less conical. 



P. thyroides Say. Common at both places, abundant on the hill- 

 top at M; rather large, with strong shell and lip. 



P. pennsylvanica, Green. A few at P, shell rather high. 



P. mitcheUiana Lea. One at P, found by Dr. Ortmann. 



P. paHiata Say. A few at P. 



P. nppressa Say. Common at M, mostly young; abundant at P, 

 mostly dead shells. 



P. iirftecta Say. Common at P, quite small, diam. 9.5-10.5 mill.; 

 color from light to brownish. 



P. tridentata juxtidens Pils. Common at P, small, with a narrow 

 umbilicus, strong lip and high parietal lamina; the curve between the 

 upper and lower " teeth " of the peristome is narrow and rather angu- 

 lar at the periphery, and in most specimens there is an additional thin 

 lamella extending downward and inward from the upper tooth. 

 From ^ts whole configuration this form appears to represent a 

 variety. 



P. fraterna Say. At both places. In some specimens the umbili- 

 cus is covered or nearly so, in others rather open, and the base 

 around the umbilicus is rather excavated, as in P. monodon (leai). 

 The surface of all is finely and densely hirsute, and the color is light 

 brown. 



P. stenotrema Fer. Common at P. There are two forms, one of 

 them with a large notch in the peristome, and also otherwise differ- 

 ent, as also seen from other places; a few notes on them will follow. 



Bifidaria conlracta Say. One at M. 



B. tappaniana Ad. One at M. 



NOTES ON ORIENTAL UNIONID.E. 



BY L. S. FRIKRSON. 



The following notes are offered as so many "addenda et corri- 

 genda" to Mr. Chas. T. Simpson's great work," The Synopsis of 

 the Naiades: " 



