In comparing the Conodonts with the teeth of fishes, they present most resemblance to the minute conical recurved teeth of the genus Rhinodon of Smith : they more remotely resemble the conical, pointed, horny teeth of Myxinoids and Lampreys in that class : and the absence of any other hard part in the strata containing the Conodonts tallies with the condition of the cartilaginous skeleton ; but not more than it does with the like perishable soft condition of annelidous worms and naked mollusks. Rhinalon has very small teeth, "en brosse," of a simple conical recurved form : there are 12 or 13 teeth in each vertical row, and about 250 such rows in each jaw : so that each fish may have from 6000 to 7000 teeth. But the teeth of _Rhinodon have not the basal extensions and processes of many of the Conodonts ; and the teeth of all known Cyclostomes are much less slender and are less varied in form than in the Conodonts. Certain lingual plates of Myxinoids are serrate, but not with a main denticle of much greater length—such as shown in the form of the Conodont called Ma,chairodus by Pander. Most cyclostomous teeth are simple, thick cones, with a subcircular base ; and every known tooth of a cyclostomous fish is much larger than any of the forms of Condon, which rarely equal half a line in length. This minuteness of size, with the peculiarities of
form, supports a reference of the Conodonts rather to some soft invertebrate genus. Certain parts of small Crustacea e. g., the pygidium or tail of some minute Entomostraca resemble in shape the more simple Conodonts ; but when we perceive that these bodies occur in thousands, detached, with entire bases, and that any part of the carapace, or shell of an Entomostracan or other Crustacean, has been rarely detected in the lower Silurian Conodont beds, it is highly improbable that they can have belonged to an organism protected by a substance as susceptible of preservation as their own substance. Much more likely is it that the body to which the minute hooklets were attached was as soluble and perishable as the soft pulp upon which the Conodont was sheathed. The writer finds no form of spine, denticle, or hooklet in any Echinoderm, and especially in any soft-bodied one, to match the Conodonts; and concludes that they have most analogy with the spines, or hooklets, or denticles of naked Mollusks or Annelides. The formal publication of these minute ambiguous bodies of the oldest fossiliferous rocks, as proved evidences of fishes, is much to be deprecated.