306 G. J. HINDE ON CAMBRO-SILURIAN 
of Annelids may be conclusively shown by the discovery, by the 
writer, of these Annelidan structures in the same strata with Cono- 
donts, from which the former can readily be distinguished by their 
chemical composition and their resemblance to the jaws of existing 
Annelids. Against the probability of the Conodonts having been 
the teeth of naked Mollusks, it may be noted that the former are 
principally composed of carbonate of lime, and that it is highly im- 
probable that naked Mollusks should have abounded without any of 
their shell-bearing relatives having been also present (and of these 
in the Conodont-bearing beds of the Devonian there are no traces) ; 
nor can it be supposed that their shells can have been removed by 
solution when the most delicate structures of carbonate of lime 
have remained intact. 
It has been shown that whilst Conodont teeth do not correspond in 
minute structure with, and are far more varied in form than, the teeth 
of any known fish, they yet approach closest to those of the Myxinoids. 
As it is not at all improbable that there was in Paleozoic times 
as great a development of the Cyclostome Fishes as of the Ganoids 
and Elasmobranchs, with a consequent great amount of variation 
in their structural development, we could hardly judge, from their 
pauperized descendants of the present day, how far this variation 
may have extended in former times. We should not, therefore, on 
account of the imperfect analogy of the Conodonts with the teeth of 
existing Myxinoids, reject altogether the probability that they may 
have belonged to a similar low type of Fishes. At present, how- 
ever, the facts at hand appear insufficient to decide the question. 
Owing to the uncertainty respecting the animals to which the 
Conodonts belonged, any arrangement of the teeth themselves must 
almost entirely rest on an artificial basis, and consequently possess 
little zoological value; detailed descriptions and figures, however, 
such as those given by Dr. Pander, are of great importance and 
service for paleontological reference ; and for this purpose I have 
attempted to give a similar detailed account of the American forms, 
commencing with those from the earliest formation in which I have 
met with them. 
1. Conodonts from the Chazy Formation. 
Genus Prronropus, Pander, 1856. 
PRIONIODUS RADICANS, Hinde. (PI. XY. figs. 1-6.) 
The central tooth relatively very long and robust, and gradually 
tapering to a point, either straight or with a more or less dextral 
or sinistral curvature. ‘The lower portion is produced below the 
position of the lateral denticulate extensions, to form a single blun- 
ted termination or two or three small fang-like projections. The 
front portion is strongly convex in section, but nearly flat at the 
back, and a deep longitudinal groove extends at the back of the 
tooth from near the tip to the base. The lateral extensions, spring- 
ing more or less obliquely from both sides of the main tooth, are 
narrow, straight, or slightly curved, strongly convex in front and 
