TEETH OF DIPHYODONTS. 305 



succeeding teeth, the four last have multicuspid crowns like true 

 molars. Potamogale ' has — 



. 3.3 0.0 3.3 3.3 

 \'*.3 ; C 0.0 ; '' 3^3.3 = 36 ' 



In this large otter-like piscivorous shrew the anterior tooth of 

 the premolar series, in the above formula, may be homologous 

 with the canine in fig. 242 ; the double fang of the upper one 

 would not bar such determination. The posterior incisors and 

 the premolars have triangular trenchant crowns like the teeth of 

 some sharks : the anterior upper, and the second lower, incisors 

 are large and prehensile, as in Solenodon. 



The typical Shrews always manifest their rodent analogy by 

 the great preponderance of the anterior pair of incisors in both 

 upper and lower jaws (vol. ii. p. 277, fig. 155 3 ). In the lower jaw 

 the great incisor, ib. 2, i, is uniformly succeeded by two small, 

 p 3, 4, and three lanre, m ], 2, 3, multicuspid molars; but in the 

 upper jaw the number of small premolars varies. The last true 

 molar is commonly of small size. The subgenera of Shrews are 

 chiefly based upon the form of the large incisors and the numerical 

 variations of the dentition of the upper jaw. In the common Shrew 

 (Sorex araneus, Linn.) there are three true molars and four small 

 teeth between these and the anterior incisor; this tooth, ib. 1, i, 

 has a pointed tubercle at the back of the base of the crown. The 

 long procumbent incisor of the lower jaw has the trenchant supe- 

 rior margin entire. In the Sorex (Amphisorex) tetragonurus, the 

 upper edge of the lower incisor is notched ; the large upper incisor 

 appears bifurcate from the great development of the posterior 

 talon ; five small teeth, progressively decreasing in size, intervene 

 between the upper large incisor and the true molars. In the 

 Sorex (Hydrosorex) Hermanni, the trenchant edge of the lower 

 procumbent incisor is entire ; there are four small teeth between 

 the large anterior incisor and the true molars in the upper jaw, as 

 in the great Sorex indicus; but the three first are subequal, and 

 the fourth very minute ; there is a fourth small true molar above. 

 The enamelled tips of the teeth of the species of Amphisorex and 

 Hydrosorex are stained of a bright brown colour ; the teeth of Sorex 

 proper, as the common Shrew (S. araneus), are not so stained. 4 



In the progress of the formation of the large notched incisors, 

 the summits of the tubercles are first formed as detached points, 



1 Du Chaillu, an", and clxvi", p. 353. 



2 clxv", p. 6. 



8 In this figure the tooth marked p 1, being at the suture of the premaxillary with 

 the maxillary, should be the canine, c 1. 

 4 clxvii", p. 6. 

 VOL. III. X 



