1857.] FALCONER — PLAGIAULAX. 2/5 



• 



Plagiaulax that the species were herbivorous or frugivorous. I can 

 see nothing in the character of their teeth to indicate that they 

 were either insectivorous or omnivorous. 



The larger species, PL Becklesii, I have named after Mr. Beckles, 

 the discoverer, to whose energetic and well-considered explorations 

 Palaeontology is indebted for so many and important additions to the 

 Upper Oolite (Purbeck) fauna, after the efforts of the Geological 

 Survey Department, specially directed to the same object, under so 

 able a head as the late Professor E. Forbes, had proved unsuccessful. 

 This species equalled the size of a squirrel, or nearly that of Petaurus 

 macrourus'^ , one of the Flying- Phalangers. The other species was 

 very much smaller ; and, being one-half the linear dimensions, was 

 probably about one-twelfth of the bulk of the former, or near the 

 size of the " Pigmy Flying Opossum," Acrobata pygmcea. 



About the mammalian associates of Plagiaulax I abstain from 

 making any remarks beyond the few which are introductory to this 

 paper, as the fossils will so soon pass, for a detailed description, into 

 the hands of Professor Owen, who has already designated one of the 

 largest of the new forms by the generic name of Triconodon. The 

 Purbeck mammalian genera announced up to the present date are 

 therefore Spalacotherium^ Triconodon, and Plagiaulax. 



There are, however, some points of general geological interest, on 

 which I may be permitted to make a few observations. 



The first is the relation of resemblance which the molar teeth of 

 Plagiaulax minor bear to those of the Triassic Microlestes antiquus 

 of Plieninger. The agreement in general form is so close, that, had 

 detached molars of both been met with in beds of the same forma- 

 tion, they might have been taken for back and front, or upper and 

 lower teeth of the same, or of nearly allied, species. The essential 

 crown-characters are the same in both, namely, two opposed longi- 

 tudinal marginal ridges, more or less lobed or crenated, and separated 

 by an intermediate chasm or depressed discf . A solution, however 

 approximative, of so ancient and obscure a mammal as Microlestes 

 is not devoid of interest. Plieninger considered it to be predaceous, 

 hence the name ; other naturalists were disposed to regard it as 

 leaning, however remotely, to the omnivorous Pachyderms, or omni- 

 vorous Insectivora ; while Professor Owen, in recognizing at once the 

 mammalian character of the teeth, admitted them to be distinct from 



* The skeleton so named in the Cat. (Osteol. Mus.) Roy. Coll. Surgs., No. 1849. 



t Judging from the very careful drawings and casts, the two teeth of Micro- 

 lestes, figured in Lyell's ' Manual of Geology,' would appear, as there surmised, to 

 indicate at least distinct species. The larger tooth (fig. 442. p. 343 of that work) 

 resembles the penultimate molar of Plagiaulax Becklesii, regarded in the side- 

 aspect, inner surface. There is in both an anterior talon, forming an accessory 

 lobule where it joins on with the anterior inner tubercle. But 1 can detect no- 

 thing in either like the basal cingulum referred to by Mr. Waterhouse {loc. cit.). 

 Fig. 441, representing the first-discovered tooth of Microlestes antiquus, crown - 

 aspect, is the one which bears the closest resemblance to the last true molar of 

 Plagiaulax minor. 



