210 BRITISH FOSSIL REPTILES. 



discovered by the Rev. Peter Brodie, M.A. F.G.S., in the upper Green-sand at Barnwell, 

 near Cambridge, and a few other specimens have been obtained by James Carter, Esq. 

 from the Green-sand of another locality, near Cambridge. 



The fine examples of teeth figured in PI. 26 (with the exception of fig. 8) were 

 discovered in 1847 by Mr. Potter, of Lewes, in the lower bed of Chalk-marl, just 

 above the Green-sand, in the vicinity of that town. They formed part of as many as 

 from twenty to thirty teeth of nearly the same size which were scattered at no great 

 distance from each other. No part of the jaw-bones could be detected ; and as the 

 teeth are fully formed, and some of them retain their long fangs, it may be inferred 

 that they were originally implanted freely, like the teeth of the Crocodile, in loose 

 sockets, and have dropped out as easily, after the decomposition of the gums and 

 other soft parts. The crown is about two sevenths the length of the entire tooth, 

 and its enamelled striated coat terminates by an abrupt and well-defined border ; the 

 fang continues to expand to about its middle part, whence it gradually contracts to an 

 obtuse end, which is perforated by the entry to the pulp-cavity. The general shape of 

 the crown agrees with that of the Polyptycliodon continuus ; the difference is shown by 

 the greater proportion of the ridges which stop short of the apex of the crown, espe- 

 cially on the convex side of the tooth. In using the term convex or concave as applied 

 to the crown, allusion is made to the slight bend of crown in the direction of its axis. 

 Around the entire basal part of the crown the ridges are close together : their inter- 

 spaces are only the clefts that separate them. On the concave side of the tooth a 

 large proportion of the ridges extend nearly to the apex, as is shown in PI. 26, fig. 1 ; 

 but on the convex side a greater number extend only one third or two thirds towards 

 the apex, these shorter ridges alternating with the longer ones, between which, there- 

 fore, at the apical part of the tooth, there are intervals of flat tracts of enamel. The 

 apex of the tooth is rather obtuse. On one side of the crown there is a long ridge, 

 towards which contiguous shorter ones have a convergent inclination. The long fang 

 of the tooth is covered by a layer of smooth cement. The dentine is compact, and 

 corresponds in microscopic structure with that of the crocodile's teeth. In the frac- 

 tured specimens of the teeth from Lewes, the dentine had become resolved into super- 

 imposed conical layers, as in the larger tooth from the Green-sand of Maidstone : this 

 effect of long interment is represented in figs. 1,3, 5, and 7, of PI. 26. There is no 

 trace of the absorbent action excited by pressure of a successional tooth in any of 

 these specimens of teeth. 



Although the detached state of the above-described teeth with well-developed fangs 

 would have suggested and sustained the inference that they had been implanted like 



naturelle, fig. 8, reduite au quart, fig. 9.) EUes out interiurement vine cavity conique; leur surface 

 couverte d'email jusqu'a uue certain distance de leur base, est ornee des stries en relief, longitudinales, de 

 longeur in^gale, dont deux seulement, situees aux extreniites du meme diametre, arriveut jusqu'a la 

 pointe." (p. 80.) 



