192 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 7, 



formula of the Dichodon: viz. ^■^, cj^, por d^^^^ ^?=|=44; 



and that the three incisors, the canine, the four premolars, and three 

 molars formed, as in the Anoplotherium, one continuous unbroken 

 series on each side of both jaws. 



The only important matter which those specimens, owing to their 

 having belonged to an immature individual, left undecided was as to 

 the nature of the teeth occupying the position of the premolars. 

 The absence of any calcified germ beneath those teeth, in the lower 

 jaw, coupled with the advanced development of the second true molar 

 in the lower, and of the third true molar in the upper, jaws, inclined 

 me at first to regard them as permanent teeth. A subsequent recon- 

 sideration of their characters led me to interpret the phsenomena as 

 related to a modification of the order of appearance and succession of 

 the permanent teeth in the extinct genus*. I accordingly looked 

 for additional specimens to obtain a knowledge of the characters of 

 the premolar teeth, and of the permanent incisors and canines. 



A portion of the upper jaw of the Dichodon cuspidatus, from the 

 Hordwell sand, in the collection lately purchased of Lady Hastings 

 by the British Museum, exhibits the three incisors, a canine, and 

 the three anterior premolars of an adult individual, and, to judge by 

 the degree in which the crowns of the teeth have been worn, of an 

 aged one. 



The first incisor, fig. 4, i 1, has a crown 4^ lines in breadth : its 

 summit is worn flat, as far down as nearly to the level of the posterior 

 ridge circumscribing the cavity which still remains at the outer and 

 back part of the crown. The pointed, narrower, outer extremity of 

 the crown overlaps the anterior facet of the outer side of the second 

 incisor, i 2 : the crown of this tooth is less worn ; it is 4 lines in 

 breadth ; the posterior basal groove extends the whole breadth of the 

 crown. The third incisor, i 3, has been partly displaced : the whole 

 simple subcompressed root, and a part of the crown, are exposed. The 

 canine has been entirely displaced, but the crown is fortunately pre- 

 served, adherent to the matrix outside the incisors : on the right side 

 of the upper jaw the bottom of the simple socket for the root of the 

 canine is shown. The crown has a breadth of 5 lines : its exterior 

 is rather sinuous with a double convexity, as in the deciduous canine 

 with a crown of 4 lines in breadth, in the first-described specimen. 

 On the opposite side of the tooth the crown shows a polished surface 

 of abrasion, as if that side had been obliquely and cleanly cut off, 

 leaving a trace of the depression and basal ridge at the back part of 

 the inner surface. 



The form of the worn surface shows that this extended but short 

 canine must have been worked upon by the lower canine, like a car- 

 nassial tooth or scissor-blade ; but the flattened grinding surface of 

 the succeeding premolars indicates that the cutting power of the 

 canines was exercised upon vegetable substances. 



The first premolar (PI. III. fig. 4, p\) has a breadth, or fore-and- 



* " Forms and Structure of the Teeth " in " Circle of the Sciences," 8vo, 1854, 

 p. 296. 



