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Show 1876.] MR. E. R. ALSTON ON THE ORDER GLIRES. 97 3. Hydrochcerus, Brisson, Regn. An. p. 116 (1756). 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. GLIRES DUPLICIDENTATI. Incisors |-, at birth J- ; 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 process in the form of a tubercle. Clavicles complete. Ears short. Hind limbs not markedly elongated. No external tail. Palaearctic and Nearctic. Recent genus :- 1. Lagomys, G. Cuvier, Tabl. Elem. de l'Hist. Nat. p. 132 (1798). External characters those of the family ; two premolars above and below. Fossil genus:- 2. Titanomys, Von Meyer, Jahrb. fiir Mineralog. 1843, p. 393 (1834). One premolar only, both above and below. Family II. LEPORiDiE. Three premolars above, and two below ; grinding-teeth as in last family. Skull compressed; frontals with large wing-shaped postorbital processes ; facial portion of maxillaries minutely reticulated ; basisphenoid with a median perforation and separated by a fissure 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). Recent genus:- PROC. ZOOL. Soc-1876, No. VII. 7 |