528 Dr. C. I. Forsyth Major on the 



Sohnodon cuhanus. — Thomas* writes the tooth-formula 

 of Sohnodon as follows : — 



n 2 3 



M.\ 



(12 3' 



P.d. 3 {(xuct.) in the lower jaw is inadvertently omitted in 

 the original. 



According to this author, therefore, in both upper and 

 lower jaws only the two posterior milk-premolars are pro- 

 duced. P. 3, Hens. (P. 2, auct.)^ is stated to be absent, and 

 P. 4, Hens. (P. 1, auct.), to be present ; this interpretation is 

 due to the fact that the foremost P. is stated not to be 

 changed. Tliis view has been disputed by Leche f, who 

 writes the dental formula, based upou a single specimen that 

 he examined, as follows : — 



(2 3 4 (12 3 



)0 3 4 ) 



(234 (l 2 3 



It is consequently assumed that in both upper and lower 

 jaws only the two posterior milk-premolars are present, and, 

 moreover, that in the lower jaw the posterior I.d. is absent. 

 In addition to this Leche points out as a fact especially 

 worthy of note that all milk-teeth are of simpler structure 

 than the corresponding teeth of the permanent set. In the 

 young specimen of 8. cuhanus before me, the molars are 

 indeed fully developed, but are not yet completely protruded 

 from the jaw -, the main cusp of M. 3 sup. is beginning to 

 come through the gum. 1'he lower molars are somewhat 

 further advanced. Of the incisors three I.d. are present above 

 and below ; the lower I.d. 3 is situated on the outside and in 

 front of the considerably larger /. 3 (which is in the act of 

 coming through) and is about to be shed. The C.d. are 

 present above and below. Of milk-premolars the two poste- 

 rior are present in both upper and lower jaws ; the P. 3, Hens., 

 are showing. According to these facts I do not consider that 

 we are justified in denying that the latter have precursors ; 

 on the contrary, it is probable that in the two young specimens 

 at present known P.d, 3 has already been shed, like I.d. 3 in 

 Leche's example. As we have seen, in the Centetid^ P.d. 3 

 is always the first among the milk-premolars to be shed ; 

 since tooth-change sets in earlier in Solenodon, I suspect that 



* Proc. Zool. Soc. Lond. 1892, pp. 604-505. 

 t Anat. Anzeiger, xiii. 1897, p. 523. 



