52 Thirty-sixth Report ok the $tate Museum. 



One of the most noticeable and interesting examples of a departure 

 from normal conditions is sinistrality. With some genera and species 

 (Partula, Achatinella, Bulimus, etc.) the dextral or sinistral shells 

 occur indifferently. Thus, from a sinistral specimen of Campeloma, 

 Raf. (Melantho, Bodw.) were taken two sinistral fry. The remaining 

 twenty-five were dextral. Also, some of the fry of dextral individuals 

 are very often sinistral. In other genera only certain {supra) species 

 are sinistral, and again in some entire genera (Physa, Clausula, etc.) 

 this is a constant feature. Many genera and species have not yet fur- 

 nished a single example. Two remarkable sinistral forms are given in 

 the present paper. Several others, among our land and fresh-water 

 shells, are known from the State of New York, but not in the vicinity 

 of Albany. Individuals are found among our uniones which have the 

 cardinal and lateral teeth interchanged in the valves, thus giving to 

 the right valve the form and number of teeth belonging to the left. 

 This kind of sinistrality is of unusual occurrence, and has been rarely 

 noticed. 



Upon the authority of Professor R. Ellsworth Call, I am able to cite 

 the following species in which he has observed the above reversion of 

 teeth : Unio complanatus, Mohawk, N. Y.; U. rubiginosus, Des 

 Moines, Iowa, and U. cahawiensis, Oahawba river, Alabama. He has 

 also had the kindness to make several valuable suggestions and correc- 

 tions in the subject matter of the present paper. 



DESCRIPTION OF SPECIMENS. 



Physa anctllaria, Ray. 

 Plate I, figs. 6-8. 



Figure 6 represents a specimen with an unusually expanded aper- 

 ture. The first thickening of the labrum is immediately succeeded 

 by another thickening of the margin, which is also flexed outward 

 and produces the enlargement. 



The second specimen, figure 7, exhibits the tendency of the outer 

 volution to become free. The suture is very deeply impressed nearly 

 to the columella, and the aperture is much shortened. 



These two specimens exhibit natural departures, while figure 8 rep- 

 resents an accidental deformity, in which the margin of the aperture is 

 deeply excavate and the lower part of the labrum is sinuate. 



