Mr. W. King on the Tctrabranchiate Cephalopods. 271 



portion to tlieir height, and tapering to sharper summits, which 

 however are obtuse and bitid. The breadth of the tooth shghtly 

 increases to the posterior pair of eminences, whilst in the Mas- 

 todon longirostris and angustidens the crown maintains the same 

 breadth, or more commonly becomes narrower from the anterior 

 to the posterior pair of mastoid eminences. 



Other differences observable on a minute comparison are too 

 trivial to deserve notice, especially when observed in only a single 

 example of a complex molar tooth. In the Australian specimen 

 under consideration the mastodontal characters are unmistakeable, 

 and the resemblance to the molar teeth of the Mastodon angus- 

 tidens is very close. The specific distinction of the Australian 

 Mastodon rests, at present, only on the slight diiferences pointed 

 out in the form of the mastoid eminences and the contour of the 

 crown of the molar tooth. 



The question may arise, whether identity of generic characters 

 in the molar teeth of an extinct Austrahan mammal with those 

 of the Mastodon can support the inference that the remaining 

 organization of the Proboscidian Pachyderm coexisted with such 

 a form of tooth ? The analogy of the close mutual similarity which 

 exists in the molar teeth of the Tapir, Dinothere, Manatee and 

 Kangaroo suggests the surmise that the mastodontal type of 

 molar teeth might also have been repeated in a gigantic jMarsu- 

 pial genus which has now become extinct ; and such an idea na- 

 turally arose in my mind after having received evidence of the 

 marsupial character of the Diprotodon and Nototherium *, two 

 extinct Australian genera, with the tapiroid t}^e of molars, re- 

 presented by species as large as a Rhinoceros. 



The more complex character of the molars of the Mastodon, and 

 the restriction of that character, so far as is now known, to that 

 genus only, makes it much more probable, however, that the molar 

 here described belonged to a true Mastodon, and the species may 

 be provisionally termed Mastodon australis. 



London, Ausiist 22, 1844. 



XXXY. — An Attempt to Classify the Tctrabranchiate Cephalo- 

 pods. By William King, Curator of the Museum of the Na- 

 tm-al History Society of Northumberland, Durham, and New- 

 castle-upon-TjTie. 



The follovv'ing observations on the Tctrabranchiate Cephalopods 

 are in substance the same as some which formed part of two lec- 

 tures which 1 delivered in the autumn of 1841 in the Theatre of 

 the Literary and Philosophical Society of Newcastle-upon-Tyne. 



* The characters of these genera and the evidences of their marsupial 

 nature will be the subject of a future communication. 



