428 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuUC 7} 



d 7. The specimen so marked is a portion of the so-called ' dirt- 

 bed,' from the Purbecks at Durdlestone Bay, having imbedded in it 

 the right ramus of the lower jaw of the Spalacotherium, wanting the 

 ascending branch, but containing one incisor, a canine or canine- 

 shaped premolar, and ten succeeding molar teeth. It is represented 

 of the natural size in outline, and magnified in tint, in fig. 10. 



Fig. 10. — Right ramus of the lower jaw, with teeth, of the Spala- 

 cotherium TRiCTJSPiDENS, Owcu. (Nat. size, and magnified.) 



O::^^^^^^^^^ 



a. Oblique view of the molar tooth No. 8. c. Laniariform tooth (=first premolar ?). 



6. Crown of the same, seen from above. i. Incisor. 



The incisor, i, is the smallest of these teeth, and has a subquadrate 

 or very obtusely-conical crown, convex externally. The canine or 

 canine-shaped premolar, c, is more than twice as long and broad as 

 the incisor, with a subcompressed, sharp-poiated conical crown, a 

 little inclined backwards ; it appears to have been inserted by a 

 divided root, like the similarly-shaped and proportioned first pre- 

 molar in the Mole. The two succeeding teeth, 1 & 2, are one-third 

 smaller than the canine, with subcompressed, conical crowns, at the 

 fore and back part of which the base is slightly produced : each is 

 implanted by two distinct fangs. The third and fourth teeth have 

 a similar form and complex implantation, but are somewhat larger, 

 and the basal cusps are more developed : in the fourth tooth this 

 development gives a distinctly tricuspid character to the crown, the 

 middle cusp, representing the crown of the preceding teeth, being the 

 largest and highest. The six following teeth, 5 to 10, repeat the 

 same unequal tricvispid form, with increased but varying size ; the 

 middle teeth, 6, 7, 8, being the largest, and the last tooth, 10, 

 diminishing in size in a greater ratio than the penultimate one, 9. 

 These last six molar teeth are so close together that it was difficult at 

 first to persuade oneself that they were not so united as to constitute 

 fewer and more complex molars. The lateral cusps incline inwards 

 and project from a plane more internal than the longer middle cusp. 

 The inner side of the crown presents a wide longitudinal groove at 

 the base of the middle cusp, between the inwardly inflected lateral 

 cusps : the base of the crown presents externally a well-defined narrow 



