184 DE. C. J. rOESYTH MAJOE ON MIOCENE SQUIRRELS. [Feb. 28, 



3. To the Xerus-tyi^e belong most of the semi-hypsodont 

 Sciiirme teeth o£ the groups ah'eady mentioned. It is dis- 

 tinguished from the Sciurus-vi(l[/aris-tyY>e by a more complete 

 lophodontism, the crests running in a transverse direction, and 

 tlie valleys being reduced to narro\A' but deep fissures. The main 

 difference from Ungulate lophodont molars consists in their having 

 not two, but four or even five crests, the anterior and posterior 

 margin of the molar l)eing as much or almost as much raised as 

 the two medial crests. So that the Ttr»s-iype presents in upper 

 as well as in lower molars tlu-ee transverse depressions or fissure- 

 like valleys (and four in superior molars where there are five 

 crests). This type forms on the whole a \ery striking approach 

 to the hystricoinorphan molar. 



Twenty years ago I pointed out that two African Squirrels, 

 Sc. cotui'icus and 8v. levco^tignm (this last being now considered as 

 a variety of Sc. pi/n-ojws), approach the HystricvDmorpha in a 

 further development of the characters in Avhich the Ethiopian 

 Xents departs from the tScitfrKs-vuh/aris-iype. Again, the Eocene 

 Scini-oides was shown to resemble in its molars those of the 

 Hystricomorpha Cercolahes and Kretliizon, whilst, on the other 

 hand, the Eocene hystricomorphan Trechomi/s was shown to 

 approach >Sciuroide.<i \ 



Twelve years later, Schlosser, working on fossil forms, with 

 much richer material at his command, confirmed these observations, 

 showing that a group of Tertiary Rodentia sho^\ed characters 

 intermediate between the Sciiu'omorpha and Hystricomorpha '. 



It is of no little interest that aetually living Sciuromorpha show 

 in their dentition, as \a ell as in the characters of their skull, that 

 the distinction between Sciuromorpha and Hystricomorpha is less 

 sharp than is generally admitted. Schlosser seems not to have 

 examined any recent Ethiopian Squirrels, as he does not jnention 

 the im])ortant characters they present. Xor has any other author, 

 with the exception of Alph. Milne-Edwards, wlio incidentally 

 mentions Sciums pt/n-o/n's, F. Cuv., saying that "Ics molaires 

 offrent une apparence toute particuliere, due a I'existence de replis 

 d'i'mail qui s'enfoncent profondement dans la dentine, constituant 

 ainsi de veritables rubans. .le ne connais que cette espece sur 

 laquelle on observe ces particularites ; cependanb, chez certains 

 Xervs, on en voit des indications "' '\ 



The fact is that the majority of Ethiopian Squirrels depart from 

 the Sciurine type both in their superior and inferior mol;u-s, 

 a])proaching towards hystricine lophodonty by the uniting of their 

 cusps in a transverse direction, so that the characteristic cu])-like 



graphiea, xxxi. ISS.'i, pp. 10-102. 



' H. et Alpli. Milne-Erlwnrds, " Hecherches pour.«i.'r\ir:"i rilUtoireyafiirollo 

 cIps Mamiuifures, etc." (Paris, 18fi8-1874), p. KUj. 



