106 DEAN. [Vou. IX. 
that the lateral canal is an open one as in Chlamydoselache, 
and is bordered by stouter and more numerous denticles. The 
relation of their size to that of those of the surrounding body 
wall might be looked upon as significant of the primitive mode 
of encasement of the sensory tract. 
Tue DENTITION. 
Comparison of a series of jaws has rendered it possible to 
understand the general characters of dentition. The head of 
Cladoselache viewed from below, even in its crushed condition, 
is strongly suggestive of Chlamydoselache, especially in the 
incurving, fringing teeth of the upper jaw. Like the modern 
form, its teeth were largest, longest and most acutely pointed 
symphysially, and shortest and smallest at the angle of the 
mouth. It has apparently the two anterior rows of the upper 
jaw separated by a depression, probably toothless, passing inward 
between. It is impossible as yet to say that there existed a 
symphysial unpaired row of teeth on the lower jaw to be 
opposed to this depression. The broad horizontal bases of the 
teeth were not, however, arranged in fore and aft rows, with 
alley-ways between. 
In Cladoselache fylert each ramus of either jaw was closely 
studded with about twenty-five (ecto-entad) banks of teeth, 
each bank containing about eight teeth. 
These ecto-entad banks, as already suggested, vary in general 
character in different regions of the mouth. Each tooth is 
wedged in between its neighbors of the right and left banks so 
that one lateral denticle becomes the buttress of the main cusp of 
its right neighbor, the other denticle often going no further than 
opposite the lateral denticle of its left neighbor. The general 
curve of the jaw gives an even and close-set appearance to the 
dentition. The symphysial rows, though consisting of the 
largest teeth, have not been satisfactorily determined. Their 
outermost teeth possess an extremely long principal cusp, 
whose length is about one-ninth the distance from snout tip 
to articulation of jaw. These appear to have been greatly 
incurved, and were notably larger than their succeeding 
neighbors in the same bank. The lateral denticles were 
