434 BE. C. I. rOESTTH MAJOR OX 



through the same lacuna (" Zahnliicke "), produced by the dropping out of the first 

 deciduous. The two posterior deciduous teeth are, according to the writer, situated on 

 the top of molars I. and II. (!) respectively, like so many caps. So that, according- to this 

 description, of the five upper cheek-teeth of Frolagns, the tirst and the last liave no 

 deciduous predecessors, hut the three intermediate have. In the lower jaw Praas finds 

 two deciduous cheek-teeth : " Neben dem ersten zweiwurzeligen Deciduus, der iiber dem 

 eiuzigen Praemolaren sitzt, ist noch ein zweiter zweiwurzeliger Deciduus, der von dem 

 ersten Molaren verdrangt wird." According to this, iu the lower jaw the supposed 

 unique jiremolar and what he believes to be the first true molar Avould have deciduous 

 predecessors. 



Those astounding views necessarily created a distrust in Fraas' description of tj deciduous 

 molars (in Prolagus) ; and as a consequence most of the subsequent authors on the 

 subject, up to this day, have, with regard to the Lagomyidaj, preferred to adhere to the 

 old Cuvierian dictum, viz., that in all the Ilodents with more than three molars, only 

 the one (or more) anterior to the three ai'e replaced, and that the latter alone are to be 

 considered true molars. 



Eilhol has observed the two anterior lower cheek-teeth to change in Tifuuovtijs, and he 

 apparently extends this observation to the maxillary teeth as well : " Chez le Titanomys, 

 les deux premieres dents ^taient sujettes au remplacement " *. 



The one author who first rightly interpreted the tooth-formula of Lagomyidae is Winge, 

 although he has not seen the tooth-change. Of Fraas' statements he says that they are 

 not clear, partly due to some of the premolars l)eing called molars ; and he continues to say 

 that Lagumys — which, according to him, includes the fossil " Jli/olagiis" and its allies — 



"has^ orT cheek-teeth; these are the ~ ,- , 't ,. „ or "..,'- ,. of the tvpical ~, as is seen 



from a comparison with Lcqms ; in the maxillary the three anterior teeth, in the mandible 

 the two anterior are changed " t- 



In the first part of his memoir on Tertiary Eodentia, Schlosser speaks invariably of 

 only one inferior premolar and of a fourth inferior true molar (m. 4) in fossil Lagoinyidye J . 

 but later on he gradually § arrives at the true statement of things as given in the 

 supplement to the above memoir, in the following words : — " In this group (/. e. the 

 Lagomorpha) at least the first two anterior teeth in each jaw are changed, so that we 

 must speak of two, respectively three premolars " 1]. 



My own observations are to the following effect : — 



1. Titanohnjs. — This genus has five cheek-teeth in the upper jaw. The deciduous 

 teeth arc three in the maxillary and two in the mandible, as is seen in the llott skeleton 

 described belo^v. The two deciduous inferior teeth, as mentioned above, have already 

 been figured by Filhol %. 



* Ann. Sc. Gool. X. p. 29 (1879). 



t " Om ruttcdyrenes Tandskifte " ( Yideusk. Meddcl. Natiirh. Toreuing i Kjiibenliavu f. 1882), p. 48 (1883). Sec 

 also H. AViugc, iu ' E Museo Lundii,' i. pp. 11)8, 111 (1S88). 



% ' Pala-'outographica," xxxi. p. 10 &c. (1884). § Op. cit. p. 110, Anm. 2. 



l| Palwontogr. xxxi. p 327 (1SS5). f Oj>. cit. p. 20, pi. 3. fig. 3. 



