262 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 11, 



It is intended that, when the collection is completed, the Purbeck 

 Fossils shall be made over to Professor Owen for description and 

 publication ; and, from what is already manifest, it may safely be 

 stated, that they will furnish materials for one of the most interest- 

 ing and important of the many chapters which our distinguished 

 countryman has contributed to the record of Mammalian Palae- 

 ontology. Without forestalling Professor Owen's detailed results, 

 I may be permitted to state that I have satisfied myself of there 

 being among the Purbeck fossils at least seven or eight genera of 

 Mammalia, some of them unquestionably Marsupialia, both pre- 

 daceous and herbivorous ; and others of them conveying to my mind 

 the impression, so far as the evidence goes, that they belong to the 

 Placental Insectivora, having affinities more or less remote to exist- 

 ing types. 



Having undertaken a description of one of the most remarkable 

 of these Purbeck mammal genera, in compliance with the expressed 

 wishes of Mr. Beckles, to accompany some illustrations which will 

 appear in Sir Charles Lyell's forthcoming Supplement to the 5th 

 edition of the ' Manual of Elementary Geology,' I have thought 

 it desirable to place the anatomical evidence for the results more in 

 detail than could be admitted in a brief abridgement in that work. 



The genus ^^ Plagiaulax'^ y'' which is inferred to have been her- 

 bivorous and marsupial, comprises two well-marked species, P/. 

 BecMesii and PL minor. It has been determined upon two di- 

 stinct specimens, which were among the earliest of Mr. Beckles' 

 acquisitions, each a right ramus of the lower jaw. Latterly, two 

 additional specimens f have been received of the larger form, PL 

 BecMesii, supplementing important points of evidence which were 

 wanting in the first instance. The illustrations and descriptions 

 now submitted, are derived chiefly from the two original specimens. 

 Of these, the one of Plagiaulax BecMesii, (figs. 1 & 4, «, b, and c, c?), 

 in two pieces on reversed slabs, consists of the lower jaw, right side, 

 perfect from the tip of the incisor to the proximal surface of the 

 condyle, including the ascending ramus and coronoid, with the ex- 

 ception only of the raised posterior lower margin and inflected 

 angle ; it shows three premolars {p, in) in situ, with the empty 

 sockets of the two back molars. Another specimen (fig. 7), for- 

 tunately supplies these two back molars in situ. The lower jaw 

 (also of the right side) of the other species Plagiaulax minor, fig. 15, 

 is less perfect. It contains all the teeth in situ, beautifully pre- 

 served, but it is mutilated vertically behind the alveolar border ; the 

 ascending ramus, with aU the proximal portion, being wanting. Be- 

 sides the two true molars, it contains four premolars instead of three, 

 as in the other species. 



Teeth. — Together, these specimens furnish nearly complete evi- 



* An abbreviation for " Plagiaulacodon," from TrXayios, oblique, and av\a^^ 

 groove, having reference to the diagonal grooving of the premolars. 



t A fifth specimen, subsequently acquired, is described in the sequel (See fig. 



14). 



