VERTEBRATES. 101 



The above diagnosis applies to a certain form of teeth well rep- 

 resented in the collections from various Lower Carboniferous 

 formations, and which is homologous with the long posterior teeth 

 of the upper jaw, formerly embraced under the generic term Streblodus 

 Agass. Since it is now a well established fact that the latter form 

 formed part of the dental armament of the jaws of the same fish 

 that bore the teeth represented by the original form of Cochliodus, 

 Agass., there can scarcely arise a question as to the position the 

 present form held upon the jaw. 



It may, perhaps, be deemed premature at the present time to 

 attempt the identification with the above form of other and asso- 

 ciate teeth from amongst the detached dental remains of Cochlio- 

 donts, alone contained in the collections; but there are certain 

 forms whose occurrence and intimate association in the same de- 

 posits with that above noticed, strongly suggest their congeneric 

 relations and specific indentity. Thus, there are found teeth which, 

 possessing the general characteristics attributed to the large posterior 

 teeth of the mandible of Cochliodus, may be especially characterized 

 by their more trapezoidal outline, posterior position of the median 

 lobe, narrow posterior alation, and the relatively broad flat area of 

 the neck or anterior portion of the coronal region. The latter form 

 is further distinguished by the greater or less obliquity of the out- 

 ward and backward course of the antero-lateral border, which, 

 together with the postero-lateral border, presents the same condition 

 of narrow, rounded, inbeveled enamel fold and channeled basal rim 

 observed in connection with the opposite maxillary teeth, with which 

 they also agree in the degree of inrollment and longitudinal convex- 

 ity of the coronal region. The neck or anterior area is nearly plane 

 *or faintly swollen transversely, sometimes with a slight depression 

 near to and parallel with the antero-lateral border. The posterior 

 alation is narrow and separated from the median lobe by a compar- 

 atively narrow depression. The inner margin is moderately concave 

 in passing the posterior depression, broadly arched round the base 

 of the coronal prominence, and thence to the anterior angle more 

 gently curved or nearly straight. The relative proportions of the 

 teeth are laterally narrower and stouter than the maxillary posterior 

 form. 



There are associated with the two most numerously represented 

 species of the genus a form of teeth, which from their general 

 appearance and apparent identity of coronal structure, we have pre- 



