iiSS Owen — On the Teeth of Cochliodonts. 



Gochliodus contortus, Ag. (PL III, Figs. 1, 4, 5), as well as with 

 those of Cochliodus magnus, Ag. (now Tomodus) and Gochliodus 

 striatus, Ag. (now Xystrodus) ; it retains, however, the present 

 restricted generic characters of Cochliodus, and I indicate the species 

 under the name of Cochliodus compactus ; the predominance of the 

 ■middle (2) over the anterior (4) and posterior (3) lobes giving the 

 grinding surface of the tooth a more compact and simple character. 



The specimen of the teeth in situ of Cochliodus contortus, Ag. (PI. 

 in, Figs. 1 and 2,) is from the Carboniferous Limestone at Bristol, 

 and forms part of the collection of the Kev. Professor Sedgewick, at 

 Cambridge. 



In Plate III., Fig. 3, is figured a small portion of the mandible or 

 lower jaw, with the third tooth, c, of the right side, and part of 

 that tooth of the left side, of Streblodus oblongus, Ag. The third lobe 

 forms a larger proportion of the tooth in this genus then in Cochlio- 

 dus and gives a greater proportionate length to the breadth of the 

 grinding surface of the entire tooth. The anterior lobe is repre- 

 sented by a mere seam. The middle lobe, commencing narrow, pro- 

 minent, and ridge-like, externally expands, and subsides to a moderate 

 convexity as it bends backward and inward over the jaw. The 

 third lobe much more rapidly expands as it rises from the outer 

 apex to arch over the inner side, where it has a wavy margin, an inch 

 in extent, in a total length of grinding surface of one inch, seven 

 lines. The upper convex surface of this third lobe shows the chief 

 area of attrition. The portion of the jaw preserved shows a large 

 and deep cavity within and behind the third tooth, which probably 

 lodged the matrix or germ of its successor. The symphysis of the 

 jaw was shorter and the rami met there at a more open angle in 

 Streblodus than in Cochliodus ; the anterior ends of the last crushing 

 •teeth came into contact at the back part of the symphysis. What 

 were the proportions of the homologues of a and 6 in Cochliodus 

 (fig. 1), or whether both or either were developed in Streblodus, the 

 mutilated outer or fore part of the symphysis, in this specimen, does 

 not permit to be determined. 



The present specimen (PI. III. Fig. 3.), is from the mountain- 

 limestone of Armagh ; and forms part of the collection of the Earl 

 of Enniskillen, at Florence Court, Ireland. 



The most completely preserved specimen of the mandible of a 

 Cochliodont is that of the Tomodus convexus (PL lY. Figs. 2-5,) from 

 the carboniferous limestone of Bristol. Apparently the whole of the 

 dentary part of the right ramus and the anterior half of that of the 

 left ramus are here shown (Fig. 2). The posterior end of the right 

 dentary is of little breadth and depth, but it gains in both, and 

 chiefly in the latter dimension, as it approaches the symphysis, and 

 there rapidly acquires great breadth and thickness. The lower 

 border (Fig. 3), is thick and rounded ; the outer side, (Fig. 4) mode- 

 rately convex ; the inner side, (Fig. 5) somewhat wavy, being con- 

 cave lengthwise at its middle part. The hind part of the symphysis 

 extends back like a shelf (Fig. 2), from below the dentigerous surface 

 of that part of the mandible. 



