128 THE NAUTILUS. 



Dall 1 remarks of P. campanulatus rudentis: "Very similar 

 specimens were obtained from Anticosti, and from Marl Lake, 

 Michigan, in which the coil is even more irregularly wound, a 

 condition I take to be pathological." 



Bryant Walker 2 remarks of P. multivolvis: " When it (i. e. 

 the abnormality) occurs, it bears the appearance of an abnormal 

 extension of the last whorl being more or less irregular in form 

 and usually deflected from the plane of the rest of the whorls; ' 

 and adds that occasionally P. campanulatus has a similar ab- 

 normality. This would appear to be the closest approach to 

 No. 8 in the plate accompanying this paper. 



Dr. Frank C. Baker 3 describes P. campanulatus smithii. This 

 species would seem to be very similar, with regard to the de- 

 flection of the last whorl, to the ones discussed here, but the 

 whorls of that variety are "strongly carinated above and below, 

 the last whorl being particularly so marked." This serves to 

 distinguish the forms. Mr. Baker observes, however, as in the 

 specimens from Blue Sea Lake, the presence of the typical form 

 of P. campanulatus which shows marked variation toward the 

 gmithii type. 



Robertson 4 states: "Often distorted so that the tops of the 

 whorls are inclined at various angles. Varies considerably in 

 the length of campanulate expansion and thickness of shell." 

 This is of interest because the area, which his report covers, lies< 

 within the Archaean region of Georgian Ba3 r , where similar 

 conditions to those at Blue Sea prevail. 



Tryon 5 describes and illustrates an abnormal specimen of 

 Planorbis bicarinatus, which has developed in exactly the same 



'Dall, W. H. , Land and Fresh-Water Mollusca, Harriman Alaska Ex- 

 pedition, vol. XVIII, p. 90. 



'Walker, B. , Mollusca of Michigan, NAUTILUS, vol. 6, p. 136. 



s Baker, F. C., A New Planorbis from Michigan, NAUTILUS, Yol. 26, 

 p. 119. 



4 Robertson, A. D. , Mollusca of Georgian Bay, Contributions to Canadian 

 Biology, Supp. 47th Annual Report, Dept. of Marine and Fisheries, Fish- 

 eries Branch, Pt. 2, p. 101. 



5 Tryon, Geo., Jr., An Abnormal Specimen of Planorbis bicarinatus. 

 Jonrn. of Conchology, vol. 2, p. 3. 



