1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 9/ 



3. Ht/drochoerus,Bnssoii,'R^n.An.p.ll6 (1/5G). 



Body massive ; limbs moderate ; muzzle very blunt ; eyes and ears 

 small ; tail obsolete ; hair coarse and sparse ; all the feet fully webbed. 

 Skull massive; malar very deep; palate produced behind the last 

 molar ; incisive foramina short ; paroccipital processes very large and 

 long. Upper incisors grooved in front ; upper grinding-teeth each 

 with two lobes, united only by cement, except the third molar, which 

 has twelve narrow transverse plates ; lower premolar and first molar 

 with three narrow lobes, the second and third with four. 



Suborder II. Glues duplicidentati. 



Incisors 4> at birth 4 ; the outer upper incisors soon lost ; the next 

 pair very small, placed directly behind the large middle pair ; their 

 enamel continuous round the tooth, but much thinner behind. Skull 

 with the optic foramina confluent, with no true alisphenoid canal ; 

 incisive foramina usually confluent ; bony palate reduced to a bridge 

 between the alveolar borders. Fibula ankylosed to tibia below, and 

 articulating with the calcaneum. Testes permanently external ; no 

 vesicular glands. Two families : — 



Family I. Lagomyid.e. 



Either one or two premolars above and below ; grinding-teeth 

 rootless, with transverse enamel-folds dividing them into lobes. Skull 

 depressed ; frontals contracted, with no postorbital processes ; facial 

 surface of maxillary with a single perforation ; posterior angle of 

 malar produced almost to the auditory meatus ; basisphenoid not 

 perforate, nor separated by a fissure from the vomer ; coronoid pro- 

 cess in the form of a tubercle. Clavicles complete. Ears short. Hind 

 limbs not markedly elongated. No external tail. Palsearctic and 

 Nearctic. Recent genus : — 



1 . Layomys, G. Cuvier, Tabl. Elem. de l'Hist. Nat. p. 132 ( 1 JOS). 

 External characters those of the family ; two premolars above and 



below. 



Fossil genus : — 



2. Titanomys, Von Meyer, Jahrb. fur Mineralog. 1843, p. 393 



(1834). 

 One premolar only, both above and below. 



Family II. Leporid.*. 



Three premolars above, and two below ; grinding-teeth as in last 

 family. Skull compressed ; frontals with large wing-shaped post- 

 orbital processes ; facial portion of maxillaries minutely reticulated ; 

 basisphenoid with a median perforation and separated by a fissuie 

 from the vomer ; coronoid process represented by a thin ridge of bone. 

 Clavicles imperfect. Ears and hind limbs elongated. Tail short, 

 bushy, recurved. Cosmopolitan (except Australasian region). Re- 

 cent genus : — ■ 



Proc. Zool. Soc—1876, No. VII. 7 



