266 FISHES CHAP. 
imperfect truncated cones with their apices directed backwards, 
the successive cones adhering so closely to one another that they 
combine to form a central conical chamber with a spirally disposed 
cavity winding round it. In D, on the contrary, the free edge 
of the valve is deflected forwards, so that, as in C, a nest of cones 
Fig. 159.—Examples of various types of the spiral valve in Elasmobranchs. A, B, C, 
and D in specimens of Raia spp.; E, in Sphyrna malleus. A, B, and D represents 
longitudinal sections of the intestine, the ventral portion of the valve being re- 
moved. In C successive portions of the ventral wall of the intestine have been cut 
out. In E the intestine has been opened along the mid-ventral line and its wall 
reflected to the right and left ; the ventral portion of each coil of the “scroll” valve 
has been removed. In most of the figures the pylorus is shown in the upper part, 
and the “rectal” gland in the lower. (From T. Jeffery Parker.) 
is formed, but the apices of the successive cones are directed 
forwards instead of backwards. Notwithstanding these variations 
in the structure of the valve as a whole, the first coil or half coil 
nearly always resembles that described in A. 
It is obvious that the structure of the valve varies consider- 
ably within the limits of the genus, and it may be added that 
various intermediate types of structure occur between A and B, 
