316 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 8, 



Genus Mastodon (Cuv.). 



Formula Dentium deciduorum. — Primores- vel - ; Laniarii — ; 

 Molar es -=8-7. 



Formul. Dent, persist. — Primor. - vel - ; Lan. - ; Prcamol. - 

 (y? )v el — ; Molar es veri - =12-8. 



Primores eburnei plerumque exserti : superiores maximi vario 

 modo porrecti, inferiores horizontales vel leviter deflexi, recti, 

 minores. Molares complicati, tritores ; coronidis rima longi- 

 tudinali obsolete bifidse colliculi concavi e tuberculis mammilla- 

 ribus per paria transverse aut alternatim dispositis, constantes : 

 adamante crasso, ccemento in valliculis parco aut subnullo. 

 Prcemolares aut cseteris forma simpliciores minores, aut nuUi. 

 Molares veri 3, deinceps majores, altero alterum extrusum a 

 tergo vicissim excipiente, demum utrinque solitarii. — Molares 3 

 utrinque intermedii (nempe deciduorum postremus et verorum 

 antepenultimus penultimusque) colliculis isomeris aut 3, 4, aut 

 5 conformes. 



Proboscis longissima, prehensilis. Corpus Yastnm artubus elevatis 

 insistens. Pedes 5-dactyli. 



Subgenus 1. Trilophodon. — Dentium molarium 3, utrinque in - 



termediorum coronis colliculis 3. 

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



termediorum coronis colliculis 4 (raro 5). 



Observations. — The adult dentition varies much in the different 

 species of the genus ; the premolars and inferior incisors being in- 

 constant. The typical complete formula is best shown by M. {Tri- 

 lophJ) angustidens of Simorre : — Incis. - ; Can. — ; Prcemol. - ; 



Mol. -=12, being identical with that of Dinotherium, so far as the 

 dentition of the latter has been determined, i. e. Incis. j ; Can. ~ ; 

 Premol. — ; Mol. j = 1 2 ; the only question being in regard of 

 upper incisors, 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 

 ante-penultimate true molar being three-ridged alike in Dinothe- 

 rium and in the section of Mastodon here called Trilophodon. Pre- 

 molars have not been met with in M. {Triloph.) Ohioticus, which, 

 counting both sides of both jaws, has 8 molars less in the adult 

 state than M. {Triloph.) angustidens ; nor have they been observed 

 in M. {Triloph.) Humboldtii. They occur probably in M. {Tri- 

 loph.) tapiroides. Their presence or absence has not yet been 

 ascertained in the other species of Trilophodon. These teeth have 

 been observed in situ in the upper and lower jaws of M. {Tetraloph.) 

 longirostrisy and in the upper of M. (Tetral.) Arvernensis. They 

 have not yet been seen in situ in the other species of Tetralophodon. 



