294 PROCEEDINGS OF THE ACADEMY OF [1892. 



raolars simple and trenchant, P4^ with a deuterocone, and p* some- 

 times witli deuteroconid Oxycl^enid^. 



2. Superior molars more or less completely quadritubercular; tri- 

 gonid of lower molars very little or not at all higher than talon ; 

 paraconid much reduced or absent; all cusps low and massive; pre- 

 molars high and acute Arctocy'Onid^.. 



3. Superior molars tritubercular, with low, massive cusps, but 

 sometimes having a well-developed hypocone on 51 2 ; trigonid much 

 higher than talon, but not forming a shearing blade; paraconid 

 reduced ; premolars high and acute TRiisODONTiDiE. 



4. Superior molars tritubercular, not trenchant ; inferior molars 

 with metaconid rudimentary or absent; talon trenchant, lacking 

 entoconid. Astragalus deeply grooved, except in Dissacus 



MESONYCHIDiE. 



5. Superior molars tritubercular and somewhat trenchant; para- 

 and metacones closely approximated, and with a cutting crest poste- 

 rior to the latter ; inferior molars with elevated trigonid, forming a 

 trenchant blade PROViVERRiDiE. 



6. Para- and metacones of superior molars connate or indistin- 

 guishably fused, protocone reduced or absent; posterior cutting 

 ridge much enlarged ; inferior molars with metaconid and talon 

 reduced or absent; the proto- and paraconids enlarged, flattened 

 and forming an efficient sectorial blade Hy^nodontid^,. 



7. Superior molars without or with only rudimentary posterior 

 cutting ridge ; para- and metacones very high and pointed and well 

 separated ; inferior molars with reduced talon, well developed meta- 

 conid ; proto- and paraconids enlarged, flattened and forming an 

 efficient sectorial blade. Face shortened PALvEONiCTiDiE. 



II. Fourth upper premolar and first lower molar forming the 

 single pair of sectorials; superior molars tritubercular, inferior 

 molars, except the first, also tubercular MiACiDiE. 



OXYCLJENID^, Fam. nov. 



Superior molars tritubercular, not trenchant; cusps erect and 

 acute ; inferior molars tuberculosectorial, with trigonid moderately 

 elevated above the talon, but not forming a shearing blade ; pre- 

 molars simple and trenchant, £4 with a deuterocone and p* some- 

 times with deuteroconid. 



The genera associated to form this family are known almost 

 entirely from the dentition, and their relationship with one another, 



