PURBECK FORMATIONS. 47 



those in the Cape Mole." ^ The corresponding teeth of the present genus and species are 

 in closer contact with each other, and are of more simple shape, and apparently more 

 simple implantation. 



The first example which I have selected from Mr. Beckles's series (PI. II, fig. 17) shows 

 the generic character of the molar teeth of Stylodon ; and, if they appear to be a little further 

 apart than in fig. 15, it is because more of the intervening matrix remains. Those who 

 have experienced by how slight a touch of the finest needle-point the crown or part of the 

 crown of a tooth flies off", in the attempt to develope these delicate fossils from their 

 subpetrified marl-bed, will appreciate the reticence which practice begets of being content 

 when enough has been exposed for comparison and determination, and of "letting well 

 alone." 



The alternative of the Cape Mole suggested in my original Memoir as preferable to 

 that of the common Mole for homologizing the teeth in place in the type-jaw, and the 

 probable nearer affinity of Stylodon to Spalacotherimn, is confirmed by the fossil now under 

 description. The two-rooted tooth with a canine-shaped and canine-proportioned crown 

 proves to be the last of the premolar series (as definable by shape). 



The instructive specimen, figured of the natural size in outline, and magnified three 

 diam. in tint, is a left mandibular ramus, wanting the rising branch, but including the 

 dental series, which may be formulised as — 



«4i:5> c YZTi'P 411^, »« 7ZZ7 = 32. 



The front or first incisor (e 1), is procumbent, with a long and narrow spatulate 

 crown. The second (^ 2), with a narrower crown, lies parallel with the first. The third 

 (^ 3) is smaller, and more erect : the fourth (^ 4) is also very small, and is nearer to the 

 canine than to the third incisor. The canine (c), with a longish slender obtuse crown 

 (perhaps not entire at the apex), slopes forward, but less so than do the incisors. The 

 outer side of the root shows a longitudinal fissure, indicative of division. 



The first premolar {p 1) is small, and near to but not touching the canine : the second 

 (p 2) rises, at an interval equal to its own breadth, from the first, and is also small. 

 The third premolar {p 3) shows a longish, subcompressed, subcurved, conical crown. 

 The fourth {p 4>) is a similar but a larger tooth. Each premolar has two roots, one 

 before the other. 



The true molar series begins, as in Amhlotlierium, by teeth of inferior size, as if they 

 had continued backward a series of deciduous teeth which the larger premolars had 

 displaced. The first molar {m 1) has a straight, vertical, smaller and more slender cone 

 than // 4 i it is also more convex antero-posteriorly, and with a cingulum extending into 

 an anterior and a posterior basal cusp. The root, or outer root, supporting the girted 

 crown, rises some way above the alveolus. These characters are repeated in the four 



' 'Quart. Journ. Geological Society of London,' 1854, vol. x, p. 425. 



