354 G. J. HINDE ON CAMBRO-SILURIAN 
large tooth is continued below the level of the base, forming one or 
more small blunted extensions; and in one of the Devonian forms 
this extension is greatly prolonged and also supported denticles. In 
other examples there is no prominent central tooth ; but a series of 
more or less similar teeth are carried on a straight or curved base. 
There are also forms with a wide basal plate denticulated on the 
upper edge, to which, in two instances, there is an appendage 
attached at right angles, and apparently of different structure from 
the toothed basal portion. Besides these more typical examples there 
are other structures, not hitherto noticed, which, from their intimate 
connexion with the teeth, evidently belonged to the same organisms. 
These are minute plates of various forms, with a longitudinal ridge 
which, in certain cases, is extended beyond the plate and has its 
upper border denticulated. ‘The plate itself is ornamented on one 
surface with small tubercles, whilst the other 1s smooth. 
All these forms, though imbedded in strata of very different 
mechanical and chemical character, as flagstones, shales, and lime- 
stones, appear to have experienced but little alteration ; they still 
retain their bright shining lustre, and the smooth and undisturbed 
outline of their bases plainly indicates that they have not been 
broken from the edges of the carapace of any crustacean. 
The very perfect condition of the extremely minute teeth in many 
of the specimens also shows that they could not have been exposed 
to any injuries from transportation. They are all very brittle and 
are slowly dissolved by nitric acid. Most of the specimens are of a 
reddish horn-colour and translucent; very rarely do they occur of a 
milky white, though this white tint is the usual condition of the 
Ohio Carboniferous specimens, and appears to have been common 
in the Russian examples. Pander regarded the white specimens as 
belonging to older individuals ; but there can be little doubt, from 
the occurrence of examples of both kinds of the same dimensions, 
that the white tint is due to some change in the chemical composi- 
tion. I find the white specimens more frequently in rocks near the 
surface, which have been more exposed to atmospheric influences. 
In many specimens, particularly those occurring in the black shales, 
while the flat base of the compound tooth is of a reddish horn-colour 
and transparent, the large tooth is nearly of an ivory-white, a 
difference which, on microscopic examination, is seen to be due to a 
different structure of the tooth and base. The Conodonts from the 
Conodont-bed at North Eyans are, as a rule, more robust and 
opaque and of a different lustre from those in the bituminous shales; 
whilst those from the Chazy limestone differ from all the rest in 
possessing a bright, glossy black tint. 
As regards the structure of the American Conodonts, an examina- 
tion of microscopic sections corroborates the result obtained by 
Pander from the Russian examples. 1 can detect the same delicate 
conical lamellar structure both in the specimens from the Chazy 
and in some of those from the Devonian; in other Devonian speci- 
mens, however, the basal portion appears to be homogeneous and 
without structure, whilst the teeth imbedded in this base have 
