(i 



skull two and a quarter inches long, and having a total length of body of eight inches, with 

 a tail of six inches. 1 



The keenness of observation and patient research with which were scrutinised, lens in 

 hand, bushels of a formation rife with organic and mostly fragmentary remains, 2 cannot be 

 sufficiently praised ; and Plieninger was worthily rewarded with this capital discovery of 

 the oldest known .Mammal. 



Sperirn 2- MiCROLESTES Moorei, Owen. Plate I, figs. 1 — 13. 



To like perseverance and qualities of discovery applied by Charles Moore, 

 Ksq., f'.G.S., to the fossils of breccia of Rhaetic bone-bed and Limestone, rilling a fissure 

 m the .Mountain Limestone at Holwell, Frome, in Somersetshire, is due the discovery 

 of teeth corresponding in size and general character with those of the Microlestes 

 (////ii/i/ns of Plieninger. 3 



These teeth, with other fossils, were submitted to my inspection in 1858, referred to 

 the genus Microlestes, and the following notes were taken of their characters. 



PI. I, figs. 1 — 4, represent (the natural size in outline, and magnified four times in tint) 

 an upper molar tooth, of which the grinding surface (fig. 1) consists of a central smooth 

 depressed area enclosed by a low thick tubercular wall. The inner side of the tooth is indi- 

 cated by the more prominent part of the wall, which is divided into three tubercles ; the outer 

 side by the lower wall with indications of subdivision into smaller and more numerous 

 tubercles, the largest forming the hind part of the wall and a great part of that end of 

 the tooth. The working surface of the crown is oblong, narrowest transversely, with the 

 inner and hinder end most produced. 



The length (vertical diameter or depth) of the crown is very short compared with its 

 breadth (fore-and-aft diameter) and thickness (transverse diameter). It is divided by a 

 well-defined constriction or 'neck' from the roots, which are four in number. Of these 

 the post-internal root is the best preserved, the other three being broken off near their base. 



A second upper molar is represented in PI. I, fig. 5, from the outer side. In this 

 tooth the enamelled crown has been worn almost to the cement-covered base. One 

 of the larger tubercles at, probably, the fore part of the crown remains. At this 

 part there are the beginnings of two fangs, or of the division of a broad anterior root ; 

 the base of a third smaller root supports the opposite end of the crown. The indenta- 



' \\ atekhouse, "Description of a new Genus of Mammiferous Animals from Australia, &c," ' Trans. 

 Zool. Soc.,' vol. ii, p. 149 pis. 27 and 28. 



2 " Eine ungeheure Masse von Zahnen, Schuppeu, Coprolitlien uud unkenutlichen Skelettheileu von 

 Fischen und Sauriern." — Op. cit., p. 165. 



3 For a description of the Rhaetic Beds of Somersetshire and an excellent account of the geology of the 

 district in which these Microlestian remains were found, see Mr. Moore's paper "On the Abnormal Con- 

 dition of Secondary Deposits," &c, in the 1 Quarterly Journal of the Geological Society of London,' 

 December, 1867. 



