1HO THE NAUTILUS. 



that this distortion upwards is not readily observed on normal 

 specimens, and any large degree of upturn of the aperture would 

 peem to be a variation worthy of note. 



VARIATION (PLATE X). 



In the form from Blue Sea Lake this tendency of the extrem- 

 ity of the last whorl has been greatly accentuated, as a study of 

 Series c in the accompanying plate will show. Fig. cl, a form 

 from Mackay Lake, near Ottawa, shows no deflection at all. 

 The others are all from Blue Sea. In this series there is a 

 gradual elevation of the extremity throughout. In c7 the lower 

 edge of the aperture is more than half-way up the preceding 

 whorl. In c8 the last whorl has been removed completely from 

 the plane of the others, and the aperture is directed upwards at 

 a high angle. The gradation throughout is such that all must 

 be considered as variations within the species, though the end 

 members are quite different. Such variation, however, if fol- 

 lowed by the disappearance of intermediate forms would result 

 in new species. 



The last shell of the series, No. 8, represents the extreme de- 

 velopment of the tendency to deflection from the plane of the 

 shell of the outer whorl. Viewed by itself, it would appear to 

 be merely a rather odd dextral form. On closer inspection it 

 proves to have four and a-half whorls to the point, where there 

 is a small campanulate expansion and where the distortion 

 commences. Therefore, so far, it is normal. The contraction 

 forming the throat of the shell is much less than usual. The 

 last whorl turns upward rapidly and, in a horizontal plane, 

 almost at a right angle to the one preceding as shown in Figs. 

 c8 and b8 respectively. In contrast to the latter, which is sub- 

 carinated above and below, the last whorl is broadly rounded 

 above, and irregularly sub-carinated below. The lines of growth 

 on the body whorl, though inconspicuous, are spaced normally, 

 and those on the small campanulate portion are much finer. 

 However on passing this enlargement, the striae become coarse 

 again, though more oblique and irregular than on the preceding 

 whorl. A short distance from the aperture the shell thickens 

 slightly but there is no pronounced expansion at the extremity 

 of this additional whorl. 



