298 PROCEEDINGS OF THE ACADEMY OF [1897. 



Halistylus circumstriatus Pilsbry. PI. VI, fig. 21. 

 Nautilus, XI, May, 1897, p. 7. 

 Maldonado Bay, iu company with H. columnus Dall. 



Ancylus Rushii Pilsbry, n. sp. PI. VI, figs. 11, 12, 13, 14. 



A small, very strongly hooked species. Aperture narrow, wider 

 anteriorly. Spire produced beyond the right margin. More elevated 

 and more curved and narrower than A. concentricus Orb. or bari- 

 lensis Moric, which are both much larger ; decidedly narrower, 

 more convex and more curved than A. obliquus, of which some 

 hundreds of examples were collected by Dr. Rush. Length 3'75, 

 breadth of aperture 1*7, height 1*5 mm. 



Creek in the " Prado," Montevideo, Uruguay. 



EXPLANATION OF PLATES VI AND VII. 



Plate VI, figs. 1, 2, 3, 4. Pisidium Sterkianum. 

 " " " 5, 6, 7. Turbonilla dispar. 

 " " " 8, 9, 10. Turbonilla Uruguayeusis. 

 " " " 11, 12, 13, 14. Ancylus Rushii. 



" 15, 16. Mesodesma Archavalettoi (Ihering) Pilsb. 

 about two-times natural size. 

 " " " 17, 18, 19, 20. Pisidium vile. 

 " " fig. 21. Halistylus circumstriatus. 

 Plate VII, figs. 21, 22, 23. Corbula Lyoni. 



" " 24, 25, 26. Corbula Iheriugiana. 



" " 27, 28, 29. Semele (Abra ?) Uruguayensis. 



" fig. 30. Thracia Rushii. 



