AND DEVONIAN CONODONTS. 363 
pound teeth is straight, narrow, elongate, and pointed at one extre- 
mity; near the opposite end is a delicate, needle-like main tooth with 
three smaller teeth on one side between it and the end of the base; 
on the other side, extending to the pointed tip of the base, is a series of 
very numerous, extremely minute denticles, appearing like a fringe 
on the upper border of the base. In some examples these small 
denticles are nearly uniform in size, in others every fourth tooth is 
larger ; but there exists considerable variation in this respect, even 
in the same specimen. In the example figured (fig. 13), of which 
the base is 1+ line in length, there are 70 of the small denticles. 
This form is very abundant and quite as widely distributed as the 
preceding. It appears to be identical with the fragmentary tooth 
named by Pander Centrodus lineatus (‘ Monographie,’ p. 31, tab. 24. 
fig. 9), from the Lower Carboniferous in Russia; it is in the same 
formation at Bedford, Ohio, and is also found at Kettle Point and 
Bear Creek, Ontario, and at North Evans, New York, in the 
Genesee Shale. 
3. Crested teeth (P1. XVI. figs. 15, 16, 17).—Of these there are two 
varieties present in Polygnathus dubius. The first (fig. 15) has the 
base compressed and nearly of equal width, save at one end, which 
isabruptly contracted. There are about twenty small teeth or crenu- 
lations on the base. The second variety (figs. 16, 17) has one part 
of the base narrow and thickened, with sometimes a row of minute 
erenulations on its upper edge ; beyond this the base forms a small, 
flattened, crest-like expansion with from 5 to 8 teeth on its border. 
Both these varieties are closely allied to the form named by Pander 
Gnathodus mosquensis (‘ Monographie,’ p. 24, tab. 2. figs. 10a, b, ¢). 
The second is the more abundant of the two, and three or four indi- 
viduals can be distinguished in the crushed example of Polygnathus. 
The small plates associated with the teeth in Polygnathus dubius 
are of an elliptical form with smooth edges (Pl. XVI. fig. 18). One 
surface is slightly convex, with a slight longitudinal median ridge ; 
the surface, as well as the ridge, is covered with small tubercles fre- 
quently with a linear arrangement ; the reverse side of the plate is 
smooth, with faint traces of concentric lines; the two ends are 
slightly elevated, and there is a median ridge with a smali diamond- 
shaped pit in or near the centre of the plate. Each plate is about 
2 line long and # line wide. Six of these plates, but all apparently 
of the same form, can be distinguished in the specimen of Polygnathus. 
Besides the teeth already referred to, there are fragments of others 
too imperfect to be recognized, and these may possibly belong to 
some forms which, occurring as detached specimens, I have described 
under other names. 
The existence of such a variety of teeth and plates in this single 
example appears to make the question of the affinities of the organism 
to which they belonged still more complex. Great numbers of teeth 
compose the lingual ribbon of many mollusks; but in none, that 
I am aware of, is there a similar variety of form, nor are there 
any bodies analogous to the tuberculated plates. Nor in existing 
Myxinoids, to whose teeth the Conodonts are comparable, are similar 
