Family HAPLODONTID^l. 



= Genus Aplodontia, Richardson and Autiiors (6ee beyond). 



< Sciurida: or Castoridw, of some Authors. 



< Castorinm, Baird, Mamm. N. Am. 1857, 350 (united with Castor in .a subfamily Castorina; of Sciurida'). 

 = Haploodontida; Lilljeborg, Syst. Ofv. Guag. Daggdj. 1866, 41 (as family of the Ilystricomorph series). 

 = Haploodontida; Gill, Arraug. Fain. Mamm. 1872, 22 (as family of a special serieR, Kaploodontoidea). 



— Haplodoniidcc, Alston, Proc. Zool. Soc. Lond. 1876, 78 (as family of the Sciuroniorph series). 



Chars.— Teeth: l.{^\- C.^; Pra.^; M §^§ = §^=^ = 22; all root- 

 less, prismatic, simple, of unique pattern of the molar crowns. Vertebra: C. 7 ; 

 D.13; L. 6; S. 5 ; Cd. 11 = 42. Seventh ce?w«/ semicostiferous, without ver- 

 tebrarterial canal. Clavicles perfect. Scapula triangular, with prominent spine 

 and well-developed acromion and coracoid. Tibia and fibula not anchylosed, 

 though closely apposed below. Ulna with long olecranon ; radius perfect, 

 admitting of rotatory movements. Carpus and tarsus each with nine bones, 

 including an os intermedium. Humerus with well-developed greater and lesser 

 tuberosities, deltoid ridge, and tubercle ; the inner condyle perforate. Femur 

 with prominent greater and lesser trochanters, glutseal ridge and tubercle. 

 A large osseous patella. Pelvis straight and narrow ; ilia prismatic, project- 

 ing beyond the sacrum. Thorax capacious, contracted anteriorly, with 13 

 ribs, 7 sternal, the first borne partly upon the last cervical vertebra. Skull 

 with no trace of postorbital processes (so conspicuous in Sciurida;), massive, 

 greatly depressed, very broad behind; zygomata widely separated behind, 

 chiefly constituted by the malars. Anteorbital foramen low in position, small, 

 oval, oblique, transmitting a fascicle of the masseter. Lachrymal large, scale- 

 like. Nasals broad, not protrusive. Mandible massive, the descending ramus 

 broadly laminar, twisted into the horizontal plane; coronoid high, falcate. A 

 large hyoid, connected with the skull by long osseous cornua. Eight lung 

 quadrilobate ; left lung bilobate. Salivary glands enormous (as in Castoridce). 

 Stomach with the cardiac portion produced into a horn-like process. Liver 

 quadripartite, the left lobe with a long process, the Spigelian lobule bifid. 



549 



