A ja C 
¢, 147 t 
The relative measurements are as follow:— 
Western Australian Shells. 
From Geographe Bay :— 
3, 73 mm. x 41 x 33 =100 x 56-2 x 45-2, 
From Esperance :— 
4. 94-mm. x 53 x 40=100 x 56-4 x 45-75. 
5. 86 mm. x 53 x 40=100 x 61 x 46:5. 
6. 81 mm. x 50 x 40=100 x 63 x 50. 
South Australian Shells. 
1. 75 mm. x 47 x 88 =100 x 62°66 x 50-66. 
2. 69 mm. x 44 x 35:5=100 x 63°77 x 51-3. 
3. 80 mm. x 52 x 41-5=100 x 65 x 51:9, 
4. 76 mm. x 50 x 41 =100 x 66 x 54. 
5. 72 mm. x 50 x 41 =100 x 69:45 x 56:95. 
6. 75 mm. x 55 x 42-5=100 x 73:3 x 56:6. 
From these data it is plain that there is an uninterrupted 
gradation between the narrow and low form of C. friendi 
to the broadest and highest example of (. thersites; and 
while the narrowest of the former kind and the broadest of 
the latter are very unlike, the intermediate examples are 
too alike to be separable, although the author of the Mono- 
graph, Cyp, in Thes. Conch., vol. iv., 1870, p. 18, writes in 
reference to them, ‘The two . . . although curiously 
allied, differ so much in proportions that they run no risk of 
being confounded with each other.’’ 
No distinctive feature can be found in the number or 
character of the teeth. The labral teeth in (’. thersites vary 
from 23 to 28, and in @. friendii from 21 to 28; the 
columellar from 9 to 15, and from 6 to 13. The spire in the 
Geographe Bay specimens is much longer than in South Aus- 
tralian CV. thersites, but in the Esperance Bay examples it is 
intermediate. Looking at the shell from above and behind, 
the ascending posterior channel in the Geographe Bay speci- 
men lies well to the right of the spire, and rising above it 
turns to the left over the spire, whereas in some of the 
South Australian shells it ascends directly to, and only to 
the point of the spire. In other examples, however, it turns 
to the right of the very short spire, while in one of the 
Esperance shells it goes directly to its apex. So with the 
lateral compression of the shell base in front and its angular 
deviation to the right, there is the same gradation. The 
width of the aperture is no diagnostic. This is as narrow in 
the extreme western form as in the extreme eastern, while 
in the Esperance specimens it is wider. The base is usually 
very darkly and completely coloured in C. friendii, while in 
O. thersites it is generally in large part white; but sometimes 
