60 Owen — On the Teeth of Cochliodonts, 



symphysis was prolonged, as in Cestracion, for the support of conical 

 or any other teeth. The absence of such conical teeth, detached, in 

 the matrix, had, indeed, led to the inference of their non-develop- 

 ment in the jaws of these mountain limestone fish. But the better- 

 preserved mandible of Tomodus convexus, Ag. 1859,^ (PL IV. Figs. 

 2-5), leaves no doubt of the short-pointed edentulous termination of 

 the symphysis a little way anterior to the series of large molars or 

 crushing teeth. The resemblance of this mandible to that of the 

 similarly endowed jaw of the elephant, is interesting, as exemplify- 

 ing the adaptive relations of bone, sustaining and working dental' 

 masses like millstones in species of classes the most remote from 

 each other in the vertebrate series. 



In the mandible of Cochliodus the teeth are, originally, three in 

 each ramus, and the primitive distinction sometimes remains longer 

 in the ' vasodentine,' or osseous basis of the tooth, than in the 'vitro- 

 dentine,' or enamel covering of the tooth.^ The anterior tooth, ih. 

 Fig. 1 a is the smallest, of a triangular form ; its chief part formed 

 by the mid-lobe or ridge, a, which is very convex and obliquely and 

 gently contorted from behind and below, upward, inward, and 

 forward, with a slight increase of breadth or, fore-and-aft diameter, 

 in this course, and with the moderately convex inner or mesial 

 border in contact with that of the tooth of the opposite ramus. 

 The anterior lobe seems to have had the form of a small tubercle, 

 but its summit is broken off ; the posterior lobe is a narrow, seam- 

 like, raised border, extending farther back on the outer side, Fig. 

 2 a, than on the inner side of the ramus. 



The middle tooth, (PL III, Figs. 1 and 2 6), is of greater transverse 

 than antero-posterior extent, and, like the foremost, consists 

 mainly of the second or mid-lobe : its crown is a longish triangle, 

 with the short base ' mesiad,' and the obtuse apex laterad, or out- 

 ward. This, in the tooth of the right side, is shown in Fig. 2 6 : as 

 it rises from this side or end the lobe is very prominent, but 

 it slightly subsides, as it expands and bends over the mandible to 

 the inner surface, where it is in contact for four-fifths of its extent 

 with the same surface of the opposite tooth, (PL III. Fig. 1 b). The 

 anterior lobe, very narrow at the outer side or apex of the tooth, 

 increases in antro-retral breadth to the inner side or base of the 

 triangle, but with scarcely any elevation. It makes, thus, part 

 of the border of the tooth slightly concave, as shown on .the right 

 side, in Fig. 1. The posterior lobe, or ridge of this tooth, h, is 

 obsolete. 



The third and largest tooth is that on which the genus and 



^ Cochliodus maffnus, Ag. 1835. 



' This structure of the teeth, recent and fossil, of Cestracionts and Cochliodonts, -was 

 microscopically determined and described in my Paper " On the Structure of Teeth," 

 Reports of British Association, 1838, p. 135. "These teeth are composed of two 

 substances, viz., an external almost colourless layer, with a finely punctate surface, 

 which represents the enamel, and a coarser dentine composing the body of the tooth, 

 and continuous with and passing into its basis of support." — lb. and Odontography, 

 p. 54. In the article 'teeth,' Cyclopsedia of Anatomy, vol. iv. 1852, these dental 

 tissues are defined xinder the names * vasodentine,' and ' vitrodentine,' p. 865. 



