A. Smith Woodward—On the Genus Synechodus. 497 
Dentition.—In Mr. Willett’s example of the dentition of Synechodus 
dubrisiensis, already referred to, about 140 teeth are displayed in 
their natural relative positions; and the fossil is shown, of twice 
the natural size, in the accompanying Woodcut, with the first and 
second teeth and one of each of the alternate succeeding series, 
still further enlarged separately. There are eleven dental series 
upon either ramus of the jaw, each of those posteriorly placed com- 
prising as many as eight or nine teeth, while those near the symphysis 
have not more than six. There is no median symphysial row of 
teeth, and the first pair (1.) is extremely small. In the latter the 
principal coronal cusp is long and slender, its height being equal 
to the entire width of the tooth; and there are two small denticles 
in front and one behind. The teeth of series 11. are nearly four 
times as wide as those of no. 1., with the principal coronal cusp still 
very prominent and flanked in front and behind by three large 
denticles and one smaller point, of which those behind are the more 
widely spaced. The teeth of series 111. are very similar to those of 
no. .; but in the teeth of series mm. and y. the principal cusp 
rapidly becomes stouter and less elevated, and there are five denticles 
in front, while only three or four can be distinguished behind. In 
serles vi. to 1x. the size of the teeth only gradually decreases back- 
wards, but the principal cusp becomes very short and stout, thus 
more resembling the lateral denticles, which are still very numerous 
and placed well apart. In these teeth, the denticles are five or six 
in number, both in front and behind. In series x. the teeth are only 
about two-thirds as wide as those of no. 1x., while those of series xI. 
are still smaller by one-half; and in both of these all the coronal 
prominences have become insignificant, though yet faintly indicated 
by a beaded contour. The base of the crown in all the teeth is 
marked by fine reticulating wrinkles, and the lower portion of 
the coronal cusps is often vertically striated. 
On comparing the teeth of this fossil with the few examples of 
S. dubrisiensis already described, one important difference will at 
once be noted. Whereas in Mr. Willett’s specimen, the most 
anterior teeth are very small and delicate, some other fossils exhibit 
teeth in a corresponding position of a very large and robust character, 
with several feebly marked denticles on each side.’ One specimen 
in the British Museum (No. 41675) suggests that the latter pertain 
to the upper jaw; and, in that case, the Brighton fossil may represent 
the lower dentition. There can be no doubt, indeed, that the two 
types belong to one and the same species; but whether the differences 
in the anterior teeth depend merely upon their pertaining to one or 
the other jaw, or whether one type is referable to the male and the 
other to the female, remains yet to be determined. The present 
writer has examined no specimen in which the small teeth and the 
robust teeth occur together. 
Axial Skeleton of Trunk.—The vertebral centra are well calcified ; 
but only the anterior portion of the body is yet known (Brit. Mus. 
1 Proc. Zool. Soc. 1886, pl. xx. fig, 3a. 
DECADE III.—VOL. V.—NO. XI, 32 
