147 



The relative measurements are as follow:- — 

 Western Australian Shells. 

 From Geographe Bay : — 



1. 81 mm. x 40 x 34 =100 x 494 x 42. 



2. 59 mm. x 33 x 26-5=100 x 56 x 45. 



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 38 =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 harrow and low form of C. friendii 

 to the broadest and highest example of C. 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 C . thersites vary 

 from 23 to 28, and in C. 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 C. 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 

 <J. thersites it is generally in large part white ; but sometimes 



