Ix SPIRAL VALVE 267 
A and C, and A and D. The individual variations are perhaps 
even more remarkable, and appear to be quite independent of age 
and sex. By way of example it may be mentioned that valves 
approximating to one or other of those represented by C and D 
occur in different individuals of Raia maculata of the same sex 
and similar in size, even in young specimens not more than three 
inches in length. 
As regards other Elasmobranchs, the common Dog-Fish 
(Scyllium canicula)' has a well-developed spiral valve disposed 
in twelve coils, which structurally represents a more highly 
developed example of the type D. The existence of considerable 
individual variation is nevertheless indicated by the fact that 
in one specimen examined the valve was intermediate between 
C and D, five of the eight cones projecting forwards and three 
backwards. In a specimen of Notidanus sp.” there were as many 
as twenty coils, which in disposition were intermediate between 
B and C, approximating, however, more nearly to B. In a 
specimen of the Port Jackson Shark (Heterodontus)* the valve 
had eight coils, and in structure was also intermediate between 
B and OC, but approached more nearly to C. Some of the 
Hammer-headed Sharks (e.g. Sphyrna malleus)* possess a type of 
spiral valve which differs considerably from any of those hitherto 
described, and is termed a “scroll” valve (Fig. 159, E). The 
attached edge of the valve pursues a straight longitudinal course, 
or at any rate only describes a half turn and back again in 
passing from the pyloric to the cloacal extremity of the gut. In 
the middle of its course the width of the valve is about equal to 
two-thirds of its length, but towards either extremity it gradually 
diminishes until the free and attached margins meet. The valve 
thus constituted is rolled upon itself from left to right, the 
successive coils being comparable to a series of cylinders placed 
one inside the other, and becoming gradually larger both in 
length and diameter from within outwards. <A similar valve is 
present in some of the Carchariidae. 
In the Holocephali (e.g. Chimaera monstrosa)’ the valve 
describes only three and a half coils, and is further remarkable 
in that the attached margin, for a considerable portion of its 
1 Jeffery Parker, op. cit. pl. xi. Fig. 5. * Ibid. p. 58. 
3 Ibid. p: 58. 4 Ibid. p. 59. 
> Ibid. p. 58, pl. xi. Fig. 6. 
