230 Dr. T. Wright on the Paleontology of the Isle of Wiyht. 



covered a portion of the left ramus of the lower jaw of this rare 

 mammal in the lower freshwater formation of the Isle of Wight, 

 containing the three true molars in an admirable state of pre- 

 servation, I am enabled to supply a description thereof. 



The crowns of all the true molars exhibit a double series of 

 sharp conical lobes ; the teeth are fixed obliquely in the jaw, 

 their crowns having a direction forwards, inwards and upwards, 

 the obliquity of the inclination increasing from before back- 

 wards ; the first and second molars are nearly alike in size, form 

 and structure ; the first, however, is somewhat smaller than the 

 second ; the crown of each tooth rises high above the ramus of 

 the jaw ; it consists of four semiconical-shaped lobes, two ex- 

 ternal and two internal, separated from each other by a deep 

 transverse and a shallow longitudinal valley ; the two external 

 lobes are sharply lanceolate ; each has a median ridge of enamel 

 and two sharp supernumerary processes or cusps, situated at the 

 external sides of the base of each lobe ; the inner surface is con- 

 vex and smooth, and as the apices of the lobes are not worn, the 

 double fold of enamel, with its intermediate dentine, is beauti- 

 fully shown in our specimen. 



The internal lobes are larger and more fully developed than 

 the external pair, but their apices do not attain the same height 

 as those of the external lobes ; their internal surface is smooth 

 and convex, their external surface is moderately concave, and 

 iuclined to a high angle ; at the base of the external surface of 

 each of the internal lobes there are two small tubercles or rudi- 

 mentary cusps : the posterior marginal surface of all the lobes is 

 slightly polished by dentrition, whilst their sharp lanceolate 

 points are not worn, from which circumstance it may be logically 

 inferred, that the lobes of the teeth of the lower jaw locked into 

 corresponding spaces in those of the upper jaw, as in the hedge- 

 hog (Erinaceus europaus), the mole (Talpa vulgaris), and other 

 Insectivora. 



The third true molar differs from the first and second in pos- 

 sessing six instead of four lobes ; the four anterior lobes are of 

 the same form and structure as those of the second molar, 

 only they are somewhat larger ; the third or posterior pair are 

 smaller than either of the others, and they have a more rudi- 

 mentary form ; the anterior cusp is absent at the base of the 

 external lobe, and the posterior cusp is a small process which rises 

 between the external and internal lobes. 



Locality. — I found this rare fossil in a bed of greenish tough 

 tenacious clay, being No. 35 of my section*, and which stratum 

 I have shown to be the equivalent of No. 14 of my section of 



* See p. 98 of these Proceedings. 



