6 BULLETIN OF THE 
row extend half-way to the apex. In the eleventh row the folds are very 
distinct. In front the teeth are symmetrical ; those farther back have 
lost some of the symmetry. Their bases look as if pulled to one side 
(backward) by the prongs. Gradually the lateral cusps become shorter, 
until in the twelfth row they are hardly more than half as long as the 
median. The cusps have become nearly erect and the striation is very 
distinct in the hinder rows. Besides the keel at each side, a similar one 
marks the front of each cusp in these rows. On these teeth the prongs 
of the base are so short as to be scarcely noticeable, only a shallow in- 
dentation remaining of the notch between them. Here the buttons are 
merged in the ridges till they appear as projections on the sides of the 
cusps, and the cusps themselves have become stouter, shorter, and more 
like the scales. The changes appearing gradually in the lateral rows 
have culminated in the last row, where the tooth has plicated enamel, 
nearly straight cusps, a median cusp twice as long as the laterals, and 
a broad rounded base without prongs or concavities and but slightly 
notched in the posterior margin. For a description of a tooth of the 
twelfth or thirteenth row, that of Cladodus mirabilis Ag. is not far out 
of the way ; in fact, it agrees so well that, if consideration was limited to 
that particular tooth, one could have little hesitation in naming the new 
species Cladodus anguineus. Possibly the bases of the teeth of C. mira- 
bilis might not accord so well. ‘Pternodus springeri and P. armatus (Pris- 
ticladodus springert and var. armatus St. J. & W.) present forms of bases 
which are intermediate between those of Chlamydoselachus and Cladodus, 
as shown in the numerous species figured by St. John and Worthen. 
The Scales. 
Plate VI. Figs. 9-13. 
Over the entire body the scales are small and irregular in size and 
shape. On the flank and belly they are polygonal plates, or depressed 
lumps (figs. 9, 10), surmounted by one, two, or three sharp promi- 
nences, the median of which is the stronger, in places becoming a keel. 
On the tail this keel is produced beyond the base as a spine (figs. 10, 
11). This spine is very sharp, has three longitudinal ridges, and 
is excavated slightly or flattened beneath. About the mouth and in 
particular around its angles the spines are larger, more conical, and more 
erect, — more like teeth (fig. 12). Each of a few of these scales has a 
small cusp on one side near its base. In the mouth, just behind the last 
row of teeth, there are spines which are more slender, and which have 
