ORDER RODENTIA. 1413 



Family Lagomyid^e. — This family includes very small Hare-like 

 Rodents, with short ears, complete clavicles, and the fore limbs not 

 shorter than the hinder. They are very char- 

 acteristic of the mountains of Central and 

 Northern Asia, but also occur in those of 

 Europe and North America. Their cheek- 

 teeth resemble those of Lepus, but the pre- 



Fig. 1291.— Left ramus of 

 i ,1 2 -j -1 the mandible (outer view) 



molars are never more than -, and may be of Lagomys visenwiensis; 



2 from the Lower Miocene ot 



reduced to _. Those extinct forms in which Eur °P e - 



1 2 



the premolars are _ have been separated from the existing genus 



Lagomys as Myolagus, and those with only Pm. _ as Tttanomys, but 



1 



it appears preferable to include all these variations in the type genus. 



The Pleistocene of Europe contains remains of some existing and 



some extinct (Z. sardus) species, and the genus is well represented 



in the Tertiaries of the Continent as far down as the Lower Miocene 



(Upper Oligocene) ; the species of the latter horizon being L. viseno- 



viensis (fig. 1291), the type of Titanomys. Fossil remains of this 



genus have also been found in the Pleistocene cave-deposits of Port 



Kennedy in the United States. 



Suborder 2. Simplicidentata. — The incisors are always -, and 



1 



have the enamel confined to their anterior surface. The incisive 

 foramina on the palate are of moderate size ; and the fibula does 

 not articulate with the calcaneum. 



Family Caviice. — This and the following five families compose 

 the section Hystricomorpha. The Caviidce, which are now exclu- 

 sively confined to America, have four anterior and three posterior 

 digits, and in the existing genera the crowns of the molars are 

 divided by enamel-folds into transverse lobes ; the number of 



1 s 



the cheek-teeth being Pm. _-, M. _. Cam'a, in which the tail is 



1 3 



absent, is represented by remains of several existing species in the 

 Pleistocene of the Brazilian caves ; while Contracavia is a much 

 larger extinct type from the infra-Pampean of South America. 

 Microcavia, again, from the Pleistocene of Argentina, presents char- 

 acters connecting it with Cavia and the following genus. Dolichotis 

 (or Cerodo?i), in which there is a short tail, is also represented in the 

 South American Pleistocene ; two species being extinct, while the 

 third (D. antiqud) may be identical with the living form. Here 

 may be provisionally placed the genera Issiodoromys and Nesocerodon 

 from the Quercy Phosphorites and Lower Miocene of France, which 



