200 BRITISH FOSSIL REPTILES. 



Genus. — Polyptychodon, Owen. 



' Odontography,' 1840, vol. ii, p. 19, pi. 72, figs. 3 and 4. 

 'Report on British Fossil Reptiles,' Trans. Brit. Association, 1841, p. 156. 



Having described in the preceding pages of the present Section the fossil remains 

 of the Class Reptilia, from the Chalk-formations, which, as in the case of the 

 Mosasauroids, are either referable or most nearly allied to species long known as 

 characteristic of those Formations ; or which, as in the case of the Chelonia, and the 

 smaller Lacertilia with procoelian vertebrae, are nearly allied to the Turtles and Lizards 

 of the present day ; I next pass to the consideration of those fossils which indicate 

 a greater deviation from modern types of the order, and which are either new, or 

 comparatively new to Science. 



In collecting the materials for my ' Report on British Fossil Reptiles ' I soon found 

 that among the evidences of that class in the Cretaceous Deposits of England, a large 

 species of Saurian was indicated by thick conical teeth, having the general characters 

 of the teeth of the Crocodile, but distinguished by the more regular circular transverse 

 section of the crown, the absence of two opposite larger ridges, and the presence of 

 numerous close-set, narrow, longitudinal ridges, continued, in some specimens, of 

 nearly equal length to within a short distance of the apex of the crown, but in more 

 specimens, of unequal length ; a comparatively small number only of the ridges 

 extending to near the apex : a few of the largest specimens of the teeth presented 

 fewer and more minute ridges, and a greater degree of smoothness and polish of the 

 enamel. Without venturing to say how far this latter character in the largest tooth 

 might be due to age, there was a general adherence of all these teeth to a type of 

 form and structure, which differed to such a degree from the type of any other recent 

 or fossil teeth, as to induce me to signify such difference by applying a generic name 

 to the extinct Reptile to which they belonged ; and I accordingly described and 

 figured them in my ' Odontography ' under the name of Polyptychodon* in reference 

 to their many-ridged or folded exterior. 



Some of these teeth in their size, and most of thcni in their general aspect, re- 

 semble at first sight the teeth of the great Sauroid fish Ilyjjsodon, of Agassiz, which are 

 also found in the chalk : but those of Polt/pfi/chodon may be distinguished, generally, 

 by the greater solidity of the crown, and the conformity of the structure of the dentine 

 with that of the Crocodiles and Plesiosaurs : the ridges also on the exterior of the 

 crown of the Hypsodon's teeth are alternately long and short, and end abruptly at 

 different, but commonly greater distances from the apex of the tooth than in Poli/jjfj/- 



* Vol. ii, p. 19 : from ttoXus, many, itriil, a fold, ohnii, a tooth. 



