162 
PROCEEDINGS OF SOCIETIES. 
Ratio of axes. 
2-11 . 
1*96 . 
2.58 . 
3-03 . 
3*45 . 
3-75 . 
4*44 . 
Angle between 
cleavage and bedding. 
Plate. 
Fig. 
. . 22° . . . . 
. . XIX. 
2. 
. . 42° . . . . 
. . XIX. 
1 . 
. . 53° . . . . 
. . XIX. 
3. 
. . 57° . . . . 
. . XVI. 
2. 
. . 56° . . . . 
. . XVII. 
1 . 
. unknown . . . 
. . XVI. 
1 . 
. . 62° . . . . 
. . XVII. 
2. 
It appears from the preceding that, with some exceptions, which conld 
he explained, probably, if the original position of the shell were known, 
the ratio of axes of the shell increases with the angle between cleavage 
and bedding; and that all the shells are probably of one species, as the 
variations of form are attributable to the distortion produced by cleavage. 
DESCRIPTION OF PLATES XVI., XVII., XVIII., XIX. 
PLATE XVI. 
Figs. 1, 2. Valves of Posidonia Becheri distorted by cleavage, as shown 
in the drawn-out condition of the rings of growth. 
If m and n denote the axes parallel and perpendicular to the 
intersection of cleavage and bedding; and 0 the angle between 
these planes— 
07? 
Fig. 1. -=3-75. 
n 
7Y? 
Fig. 2. -=3-03, 0 = 57°. 
7Z 
Locality : Old Head of Kinsale, county of Cork. 
plate xvn. 
Fig. 1. Similar to last— 
7)7 
- = 3-45, 0 = 56°. 
n 
Fig. 2. This specimen has undergone more distortion than any of the 
others, and is, therefore, more likely to be magnified by the 
species-maker into a new variety. I believe it to be simply 
jP. Becheri , after a very severe stretch— 
- = 4*44, 4> = 62°. 
n 
Locality : Old Head of Kinsale, county of Cork. 
PLATE XVIII. 
Fig. 1. P. Becheri , almost circular variety, showing both valves. The 
beds at Kush in which it is found are much distorted, but show 
no signs of true cleavage— 
