1854.] OWEN — PURBECK FOSSILS. 427 



pound structure which that part of the jaw exhibits in the Lizard 

 tribe, continued undivided, with the convex surface as it were bifur- 

 cating to include a smooth depression, the lower division or ridge, a, 

 answering to that going to the condyle and angle of the jaw, and the 

 upper one, h, to that going to the coronoid process, in the ramus 

 of the jaw of the Mole aiid Shrew. This character first led me to 

 endeavour to ascertain more of the characters of the fossil ; but 

 before meddling with this delicate and brittle but most precious 

 evidence of the Purbeck fauna, I committed it to Mr. Dinkel's care, 

 for a drawing of the part of the natural size, and a magnified view 

 of so much as was exposed of the largest of the teeth. Having 

 received these drawings with the specimen, I proceeded to expose 

 more of the crowns of the teeth, when they were found to be tricuspid, 

 the inner part of the crown being produced into a point both before 

 and behind the longer cusp which formed the chief outer division of 

 the crown, and which alone had been exposed on first view. I next 

 proceeded to examine into the mode of implantation of these teeth, 

 and found them fixed by a fang divided externally into two roots, in 

 a distinct forked socket in the substance of the jaw. The multicuspid 

 crown, the divided root of the tooth, its complex implantation, and 

 the undivided or simple structure of the ramus of the jaw, all con- 

 curred, therefore, to prove the mammalian nature of this fossil. 



Fig. 9 c is an oblique view of the anterior side of the crown of 

 the first of the four teeth, showing that the basal ridge bends up and 

 is lost upon the side of the accessory cusp. Both the posterior and 

 anterior cusps project upwards on a plane more internal than the 

 middle or chief cusp ; and the crown of the tooth, viewed vertically, 

 gives the contour represented in fig. 9 d. The four back teeth repre- 

 sented in fig. 9 progressively decrease in size to the hindmost, which 

 seems to be the last of the series. The sharp multicuspid character 

 of so much of the dental series as is here preserved repeats the 

 general condition of the molar teeth of the small insectivorous Mam- 

 malia in a striking degree : one sees in them the same fitness for 

 piercing and crushing the tough chitinous cases and elytra of insects. 

 The particular modification of the pointed cusps, as to number, pro- 

 portion, and relative position, resembles in some degree that of the 

 Cape Mole {Chnjsochlora aurea), but accords more closely with 

 that of the extinct Thylacotherium of the Oolite (Trans. Geol. Soc. 

 2nd Ser. vol. vi. pi. 6. fig. 1) than with any of the existing types of 

 insectivorous dentition. 



The minor antero-posterior extent of the crown is considerable as 

 compared with the proportion of that diameter with the height of 

 the crown in the true molars of any of the modern Moles and Shrews, 

 except the Chrysochlora. The impressions of the inner side of some 

 teeth anterior to those in place show plainly the tricuspid character of 

 the crown, and indicate also a greater number of such molars in the 

 fossil than in any of the recent mammalia, with the exception of the 

 marsupial Mynnecohius ; of this further and more important aftinity 

 of the Spalacotherium to the Thylacotherium, the following speci- 

 mens vield more decisive evidence. 



