412 Dr. R. Harlan on a new Fossil Genus o/ r Enalio Sauri. 



length of the dental bone, immediately beneath the alveolar 

 portion, on the mesial aspect of the bone ; the bottom of this 

 groove is perforated with foramina for the distribution of the 

 nerves and blood-vessels, equal in number to the teeth (i.e. 18). 



The process of dentition appears also to possess some pe- 

 culiarities ; being two series, one directly above the other, 

 both hollow (the cavities in some instances filled up with cry- 

 stallized carbonate of lime); the mode of shedding the teeth is 

 similar, but the manner in which the inferior enters the supe- 

 rior, differs from the animals above referred to ; the inferior 

 entering the cavity of the superior directly at the centre, and 

 not at the side of the body. 



The inferior series are completed before they enter the 

 upper. I could observe no appearance of a third series, except 

 indeed the cavity in the second. The teeth of this species are 

 neither conical nor striated, which is not the case in the other 

 species, excepting the tenuirostris, in which the superior por- 

 tion is smooth, curved, and conical ; the lower half striated. 



The extreme sharpness of the cutting edge of the teeth, and 

 the juxtaposition of their bodies, precludes the possibility of 

 supposing the teeth of the upper jaw to have passed between 

 those of the lower jaw, when the mouth was closed, as is the 

 case in all the animals Ave have referred to in this paper. 



The row of teeth on the inferior appear to have passed within 

 those of the superior jaw: this supposition is further strength- 

 ened by the worn appearance of the sides of the teeth. 



This arrangement of the teeth, which would require a pe- 

 culiar configuration of the jaw, together with the peculiar distri- 

 bution of the inferior maxillary nerve mentioned above, appears 

 to me to entitle this animal to rank as a new genus. In 

 many respects it approaches very nearly the Ichthyosaurus, but 

 is separated from this genus of animals by the peculiarities 

 expressed above. We propose to distinguish this animal by 

 the following name and characters. 



Saurocephalus lanciformis. 

 Generic characters. Bodies of the teeth approximated ; 

 those of the superior and inferior jaws closing like incisors. 

 Inferior maxillary nerve passing along a groove on the mesial 

 aspect of the dental bone. 



Specific characters. Projecting portions of the teeth smooth 

 and lanciform. 



Plate III. 



Fig. 1. Tooth detached. Fig. 3. The dental bone, mesial aspect. 



2. Teeth in their sockets 4 dermal aspect. 



magnified. a. a. articulating surface. 



n. The young tooth. n. Dental bone seen from above. 



On 



