GENEKIC DISTINCTIONS OF PROBOSCIDEA. 11 



in this place more conveniently elucidates the snbject-matter 

 of this niemoir. 



G-enus Mastodon (Cuv.). 

 Formula Dentium deciduorum. — Primores - vel ^ ; Lani- 

 arii K ; Molares ~ — 8-7. 



Formul. Dent, persist. — Primor.yvel-g-;iem.— ;Prcemol.-^- 

 (I? )vel - ; Molares veri | = 12-8. 



Primores eburnei plerumque exserti : superiores maximi 

 vario modo porrecti, inferiores horizontales vel leviter 

 deflexi, recti, minores. Molares complicati, tritores ; 

 coronidis rima longitudinali obsolete bifidse colliculi con- 

 cavi e tuberculis mammillaribus per paria transverse 

 aut alternatim dispositis, constantes : adamante crasso, 

 ccemento in valliculis parco aut subnullo. Prwmolares 

 aut ceeteris forma simpliciores minores, aut nulli. 

 Molares veri 3, deinceps majores, altero alterum extrusum 

 a tergo vicissim excipiente, demum utrinque solitarii. — ■ 

 Molares 3 utrinque intermedii (nempe deciduorum post- 

 remus et verorum antepenultimus penultimusque) colli- 

 culis isomeris aut 3, 4, aut 5 conformes. 



Proboscis longissima, prehensilis. Corpus vastum artubus 

 elevatis insistens. Pedes 5-dactyli. 



Subgenus 1. Trilophodon. — Dentium molarium 3, utrinque 

 intermediorum coronis colliculis 3. 



Subgenus 2. Tetralophodon. — Dent, molar. 3, utrinque 

 intermediorum coronis colliculis 4 (raro 5). 



Observations. — The adult dentition varies much in the dif- 

 ferent species of the genus ; the premolars and inferior in- 

 cisors being inconstant. The typical complete formula is 

 best shown by M. (Triloph.) angustidens of Simorre : — 



10 2 3 



Incis. y; Can. j; Premol. -^; Mol.-g = 12, being identical 

 with that of Dinotherium, so. far as the dentition of the latter 

 has been determined — i.e., Incis. - ; Can.— ; Premol.— ; Mol. 



— =12 ; the only question being in regard of upper incisors, 



o 



the presence or absence of which has not yet been clearly 

 ascertained in Dinotherium. The affinity indicated by the 

 agreement in number is corroborated by the last milk molar 

 and antepenultimate true molar being three-ridged, alike in 

 Dinotherium and in the section of Mastodon here called Tri- 

 lophodon. Premolars have not been met with in M. (Triloph.) 

 Ohioticus, which, counting both sides of both jaws, has eight 



