GLIRES OF THE SANTA CRUZ BEDS. 459 



MEASUREMENTS. No. 



Type. 1^,087. 

 Lower dentition, length 019 



" " " Pj-niy on .on 



Mandible, depth below p^ 005 .0065 



" m y 008 .008 



SCOT^UMYS Ameghino- 



Scotcewnys Amegh. ; Enumeracion sistem., etc.; 1887, p. 12. 



It is most unfortunate that this highly interesting genus should be so 

 rare as to be known only from a few teeth. The upper molars are com- 

 posed of two laminae, separated internally by a deep enamel fold or valley, 

 the breadth of which diminishes much with abrasion. In addition to the 

 two principal laminae, there is an incipient third one, in the form of a 

 process from the outer end of the second lamina. Each tooth thus has 

 much the appearance of m- in Prolagostomzts pusillus, except that the 

 posterior process is rather shorter. Of the lower teeth only p T is known 

 and in this the incipient third lamina is anterior. 



Ameghino's suggestion ('89*, 188), that genus is the forerunner of 

 Chinchilla and Lagidium is probably correct, but the material is far too 

 scanty for any satisfactory determination of this question. 



SCOT/EUMYS IMMINUTUS Ameghino. 



(Plate LXVIII, Fig. 22.) 



Scotceumys imminutus Amegh.; Enumeracion sistem., etc., 1887, p. 12. 



The single known species is very small, the length from p A to m a , in- 

 clusive, being 6 mm. ; the upper teeth are obliquely implanted and the 

 two dental series converge anteriorly, the palate measuring 2.5 mm. in 

 width at p A and 5 mm. at m a . 



SPHODROMYS Ameghino. 



Sphodromys Amegh. ; Enumeracion sistem., etc. ; 1887, p. 13. 



Of this remarkable genus I have seen only two specimens in the 

 Ameghino collection, neither of which is the type ; both are fragments of 

 mandibles, one containing p T and the other dp T . According to Ameghino 

 (89*, 170), the lower molars are much like those of Perimys, but the pre- 

 molar is entirely different from that of any other known member of the 



