Dr. H. Falconer on Fossil Mammals. 427 



lowerjaw: the dental formula being — incisors,! — 1 ; canines, 0—0; 

 premolars, 3 — 3 and 4 — 4 ; molars, 2 — 2 ; = 12 and 14 in all. The 

 author then entered into a very full detailed description of the teeth 

 and jaw' in each of the two species. Plagiaulax characteristically 

 differs from Hypsiprpnnus, — 1st, by the obliquity of the grooves on 

 its premolars, the latter genus having the analogous teeth vertically 

 grooved ; 2ndly, by having only two true molars in each ramus of 

 the jaw, instead of the usual four and occasional three, belonging to 

 recent marsupials ; 3rdly, by the considerable salient angle which the 

 surfaces of the molar and premolar teeth form, instead of presenting 

 a imiform level line ; 4thly, by the very low relative position of the 

 articular condyle. In P. Becklesii the two incisor teeth were large 

 and robust, projecting upwards at a considerable angle, and the 

 ramus of the jaw was remarkably short and deep. In P. minor the 

 incisors were more slender, pointing less suddenly upwards, and the 

 ramus was narrower and more curved. Dr. Falconer more especially 

 infers the marsupial characters of the genus, — 1st, from itsHypsiprym- 

 noid resemblances in the grooved premolars and the relative size and 

 position of the incisors ; 2ndly, from the raised and inflected fold of 

 the posterior and inner margin of the ramus ; 3rdly, the form and 

 characters of the symphysial suture. 



The author dwelt upon the peculiarly small number of the true 

 molars in this genus, — presenting, as it does, a marked special sup- 

 pression in these organs, and so offering the most specialized excep- 

 tion, amongst the marsupiata, fossil or recent, from the hitherto 

 accepted rule of the older vertebrate forms presenting the least 

 departure from the archetypal plan. He noticed also the interesting 

 fact, that the crowns of the molars of Plagiaulax presented an un- 

 mistakeable and close resemblance to those of the minute teeth of 

 the Microlestes from the Triassic Bone-bed of Wurtemberg. Lastly, 

 Dr. Falconer alluded to the fact of little lower jaws and small isolated 

 bones forming so large a proportion of the mammalian remains from 

 this thin Purbeck freshwater bed ; whilst more or less perfect skele- 

 tons of aquatic or amphibious reptiles occurred in the same deposit ; 

 and he stated that not only had he observed that in the tanks in 

 India the bones of small animals were uniformly vi^afted to the 

 margin, but that M. Lartet had lately pointed out to him that in 

 the rich Falunian deposit of Sansan, the skeletons of the large 

 terrestrial animals were found in certain parts of the lacustrine beds, 

 ■whilst in other parts, probably the old marginal deposits, the little 

 bones of frogs, shrews, &c., could be collected by the handful. The 

 author could not therefore but hope that further explorations, by 

 opening out the stratum where it was originally deposited in deeper 

 water, would yield even richer supplies of still larger mammals. 

 March 25, 1857.— Colonel Portlock, R.E., President, in the Chair. 



The following communications were read : — 



1. " On some Fish-remains from the neighbourhood of Ludlow.** 

 By Sir P. G. Egerton, Bart., M.P., F.G.S. 



This paper comprised descriptions of some specimens of fossil 



