41G 



TLAGIAULAX. 



Haying undertaken a description of one of the most re- 

 markable 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 forth- 

 coming : 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,' 1 which is inferred to have been 

 herbivorous and marsupial, comprises two well-marked spe- 

 cies, PI. Becklesii and PL minor. It has been determined 

 upon two distinct specimens, which were among the earliest 

 of Mr. Beckles' acqrrisitions, each a right ramus of the lower 

 jaw. Latterly, two additional specimens 2 have been received 

 of the larger form, PI. Becklesii, 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 Becklesii (Plate XXXIII. figs. 1 & 4, a, b, and 

 b,'d), 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 exception only of the raised 



The lower jaw contained eight molars, 

 a large and prominent canine, and one 

 broad and thick incisor on each side. 

 ' The compressed crowns of the inferior 

 molars in this Triconodon have each of 

 them three sub-equal sharp-pointed 

 cusps, rising nearly vertically into the 

 same longitudinal plane, with basal end 

 lobules, but without additional interior 

 complication. They are so arranged, in 

 a continuous and compact series, as to 

 present a uniform serrated edge, like 

 the teeth of a saw.' Similar tricuspid 

 teeth of larger dimensions indicated the 

 existence of another species of Tricono- 

 don of a more elongated form, and about 

 one-third larger in size. Dr. Falconer 

 noted the following evidence as to its 

 marsupial character. '1. The plurality 

 of true molars. 2. The strong inflected 

 angular process. 3. The most signifi- 

 cant proof is the broad salient everted 

 rim of the ridge which is decurrent on 

 the outer side from the condyle along the 

 inferior margin, exactly as in the car- 

 nivorous marsupials. 4. The marked 

 development of the mylo-hyoid groove.' 

 ' The two species of Triconodon from 

 the cutting character of their teeth, and 

 their comparatively formidable canines, 



together with the form of the ascending 

 ramus, are more like small ferine ani- 

 mals than mere insectivorous marsu- 

 pials. It is more probable that they 

 fed on prey less minute than insects.' 



Two other species had dental charac- 

 ters closely allied to those of the mar- 

 supial herbivore Htjpsiprymnus, or kan- 

 garoo rat, of Australia. 



Lastly, there were numerous remains 

 of a reptilian form, which Dr. Falconer 

 intended describing in a memoir to the 

 Royal Society, under the designation of 

 Saurcechmodon (the essential part of 

 the term being derived from alxpfit in 

 reference to the spear-head form of th« 

 teeth), when the specimens were con- 

 signed for description to Professor 

 Owen, who designated it Echinodon 

 Becklesii. (Fossil Reptiles of Purbeck 

 Strata. — Paleeontograph. Soc. 1860. — 

 [Ed.] 



1 An abbreviation for ' Plagiaula- 

 eodon,' from -nAcfyios, oblique, and av\a£, 

 groove, having reference to the diagonal 

 grooving of the premolars. 



2 A fifth specimen, subsequently ac- 

 quired, is described in the sequel (see 

 PI. xxxiv. fig. 1). 



