PLATE I. 

 Plaxorbis exacetes. 



Page 53. 

 Figs. 1. 2. Side views of two sjDecimens. showing the position and form of the 



aperture, x 9. 

 Fig. 3. A sinistral example, retaining but few of the characters pertaining to 



the species, x 9. Swamp, Greenbush, N. T. 



SOMATOG-YRES SEBGEOBOSE-. 

 Page 51 

 Fig. 4. A shell presenting a carination around the upper portion of the volu- 

 tions, and a narrow and angular aperture, x 3. 



Mohawk river. 



GlLLlA ALTILIS. 



Page 53. 

 Fig. 5. View of a biflexed specimen in which the three apical volutions are 

 dextral and the fourth or outer volution is sinistral, x 9. 



Hudson river. Albany, X. T. 



Phtsa axcillaria. 

 Page 52. 

 Fig. 6. A specimen with an expanded aperture. 

 Fig. 7. Au example in which the outer volution shows a tendency to uncoil. 



and the aperture to become circular. 

 Fig. 8. A deformed shell presenting a very deep sinus in the lower part of the 

 aperture. All natural size. Hudson ri>-er. Albany. X. Y. 



Valvata tricaeixata. 

 Page 53. 

 Fig. {>. A specimen with the volutions unrolled except at the apex, x 9. 



Island creel: Albany, X. T. 



Uxio PRESSES. 



Page 55 



Ficr. 10. A left valve, showing an unusually alated cardinal extremity, and 



absence of radiating bands on the outer Great zone of srowtli. 



Fig. 11. A small right valve of a specimen, showing two broad radiating 



undulations. The shell is also higher than normal forms. 

 Fiir. 1'2. Left valve with the anterior portion narrow and auriculate, umbo 

 oblique, and the wing much reduced. Natural size. 



' NormanskiU. 



Uhio carioses. 



Page 54. 

 Fia". 13. A very oibbous left valve, narrowed in front and flattened on the 

 ventral margins. Female: natural size. 



Hudson rirer. Albany. X. T. 



