INSECTIVORES. 413 



tooth with a simple compressed tricuspid crown is a premolar. The 

 crowns of the true molars are thin plates, flattened from before 

 backwards, with two notches on the working edge and a longitudinal 

 groove along the outer and thicker margin, which divides the outer 

 cusp into two as shown in the figure, where the middle cusp, which 

 is the largest, is seen in the interspace of the bifid external cusp : 

 the base of the lamelliform molar divides tardily into two short roots. 

 The third internal simple cusp is not present in the anterior molar, 

 and the posterior or sixth molar has a simple tricuspid crown. 

 Another anomaly, more remarkable than that of the shape of the 

 true molars, is their separation from each other by vacant intervals, 

 as in many Reptiles. The crowns of the five lower true molars are 

 compressed antero-posteriorly but are of unusual length, and have 

 the thicker margin turned inwards, with the summit divided by a 

 single notch, and the inner and lower division is subdivided into two. 

 The anterior incisor is small and procumbent : the second has a 

 larger laniariform crown ; the third is small and resembles the two 

 premolars which intervene between this and the first true molar. 

 The lower molars are separated by wider intervals than those above ; 

 the crowns of the opposing series enter reciprocally the interspaces 

 and interlock : in mastication the anterior margin of one tooth works 

 upon the posterior margin of the opposite molar. 



According to M. F. Cuvier(l) each series in the upper jaw of the 

 Chrysochlore includes I incisor and 9 molars ; and in the lower jaw 

 2 incisors and 8 molars. M. de Blainville, guided by the intermaxil- 

 lary sutures in the young Chrysoclore, regards the first three teeth 

 in each lateral series as incisors, the fourth as a canine, and the 

 remaining six as molars in both upper and lower jaws. My views, 

 as given in the foregoing description, are expressed by the following 

 formula : in. fEf, pm. |e^, m. Jrg=40. 



In the Shrew-moles of America, {Scalops), the dentition makes 

 an important step towards the normal mammalian condition by the 

 restriction of the characters of the true molars to the three pos- 

 terior teeth in each lateral series (2) : between these and the large 

 scalpriform incisor, in the upper jaw, there are six teeth, the first two 



(.1) Dents de Mammif^res, p. 63. (2) PI. 110, fig. 2. 



