PURBECK FORMATIONS. 51 



their 'harmonise,' are recognisable, but I am unable to determine any other cranial 

 element in the remaining mass of crushed fragments. 



The lower border of the mandible, as shown in the left ramus, magn. 3 diam. in 

 fig. 18 a, slopes from below forward and very gradually upward to the socket of the first 

 or front incisor, as in the specimen, fig. 17, and in Peramiis, fig. 11. The foremost tooth 

 is preserved in both rami : it is the largest of the incisors ; the crown is shaped like the 

 bowl of a narrow spoon ; it expands beyond the root, slightly bends upward and termi- 

 nates in a rounded edge ; it is moderately convex across, externally. Three teeth of smaller 

 size and more slender crown, follow ; they are implanted each by a single root, at intervals 

 rather more than their own breadth, save the second, which is closer to the first incisor. 



The fifth tooth by resumption of size of crown, though it be less broad than the first 

 incisor, suggests a canine ; but it seems to be implanted by two fangs. After an interval 

 of rather more than the coronal breadth of the canine, there is a small simple-crowned 

 premolar; after a shorter interval there is a second still smaller premolar. Then follows 

 an alveolar tract, which may have accommodated four or five teeth of larger size. The 

 molar series is resumed by six successive teeth, which terminate it. The exposed outer 

 side of the crown in the three teeth where it is entire shows the character of the true 

 lower molars of Sti/lodon, with the type-specimen of which (fig. 15) the present one agrees 

 in size. It yields valuable accession to the evidence of the characters of the fore part of the 

 raandibvilar dentition of the genus. The cement-covered outer or main fang of the largest 

 molars rises a short distance above the alveolar, and swells into a low quasi-cingulum 

 forming the base of the enamelled crown. The ultimate and last molars seem progressively 

 to decrease in length in a degree not shown in the last two molars in place in the type 

 specimen. Does this indicate an additional or eighth molar? There are two anterior 

 outlets of the dental canal, the foremost of which opens beneath the interval between the 

 canine and the anterior premolar. 



In PI. II, figure 19 gives the nat. size, and 19 A a view magn. 3 diam., of a 

 portion of a left mandibular ramus, with the base of the ascending ramus, the last two 

 molars, and the sockets with roots of the six antecedent teeth. This specimen is chiefly 

 valuable as showing the outer part of the crown in the last two molars in place. The 

 tooth rises some way above the socket, and then swells out to form the base of a long and 

 narrow-pointed cusp or cone, which terminates, outwardly, the crown of the tooth ; but 

 this, as it extends inwards, expands in fore-and-aft diameter, and develops a minute inner 

 basal cusp. Something of this kind is shown in the ante-penultimate molar of fig. 15 a, 

 which tooth may have been rotated slightly from its natural position. The sockets of the 

 six antecedent molars indicate teeth of the same relative size as those which are in place 

 in the type specimen of Stijhdon jnisillus. 



The proportion of the mandibular ramus preserved in the present fragment corresponds 

 pretty closely with that of the type specimen ; only the crowns of the molars anterior to 



