VEETEBEATES. 299 



■which changes in the mineral constituents have taken place whereby 

 their substance seems to merge into uninterrupted continuity along the 

 lines of impiugement, or whether it is the result of the co-ossification 

 of these parts in the course of the life of the animal of whose dental 

 armature they formed a part, is not so apparent from the examination 

 of this example. It is well known that in some of the existing Mylio- 

 donts, especially Aetobat is of Muller, the anterior teeth become so solidly 

 impacted in their basal portions as to present virtually the condition of 

 a solid scute capable of great resistance. And in the various other 

 genera, representatives of which occur in the Tertiary deposits, the 

 series are as often firmly cemented, the posterior or newer teeth being 

 perhaps most generally found isolated, the same as would be the result 

 in macerating an existing jaw. In other extinct families, however, we 

 meet with identical instances where two or more teeth of the same row 

 have become firmly welded together, e. g., a specimen of Chomatodus 

 elytra (X. and W. sp.) showing five or six teeth intimately united at 

 their bases, and one other marked instance represented by a beautiful 

 little form discovered by Mr. Van Hoene in the St. Louis limestone, 

 Desmiodus tumidus, amongst the many specimens of which we have 

 examined, it is no uncommon occurrence to find series of two to six or 

 eight teeth, exhibiting different stages of solidification, from those in 

 which the suture is unmistakable to those where the inferior surface is 

 nearly smooth with scarcely a vestige of division, as in the present 

 form. In noue of the latter have several contiguous rows of teeth been 

 found, and their association upon the jaw can only be inferred from the 

 outline presented by the examples of isolated rows. Hence, it is 

 extremely hazardous attempting to ascertain the character of the jaws 

 npon which these teeth were planted — whether they were of the trans- 

 verse type so characteristic of the typical Bays, or, on the other hand, 

 approached the anteriorly pointed type common to the Cestracionts, as 

 also the Cochliodonts. The extremely rapid diminution in size of the 

 teeth from behind outward, and the consequent deltoidal figure which 

 they collectively present, strikingly bring to mind the Cochliodonts, 

 and especially that group to which Prof. Agassiz applied the name 

 Psephodus, forms in which the mandibles were produced forward much 

 after the fashion of Cestracion. Presuming, on the other hand, that 

 these teeth rested upon a transverse jaw similar to that of the great 

 Carboniferous type Agassizodus, it is necessary to assume there were 

 very few rows, probably not more than three or five, in evidence of 

 which, however, the facts are as yet meagre and unsatisfactory. 



The individual teeth present characters in their ornamentation and 

 contour which readily distinguish them from other forms of Orodus from 

 the same deposits, examples of which are noticed in this report. The 



