MESOZOIC MAMMALS in 



by Marsh as parts of a coracoid and interclavicle. The peculiar 

 character of the whole dentition of these forms indicates that if 

 they are really Prototherians they cannot be regarded as primitive 

 and ancestral types. 



It would be beyond the scope of the present work to describe 

 in detail, or even to mention the names of all the members of 

 this group, and it will therefore suffice to refer to a few of the 

 principal types. Of the forms with tubercular premolars the best 

 known is the genus Tritylodon (Fig. 24), which occurs typically 

 in beds of Lower Mesozoic in South Africa, but is also known from 

 the Trias of Stuttgart. In the Stonesfield Slate, near Oxford, 

 which belongs to the lower part of the Jurassic system, and is 

 separated from the Trias by the intervening Lias, a fragmentary jaw 

 with three teeth (Fig. 27) appears to indicate an allied type, the 

 teeth having three longitudinal ridges separated by grooves. In 

 the Purbeck beds of Dorsetshire, forming the top of the Jurassic 

 system, we find another member of this group, which has been 

 described as Buhxlon, closely allied to which is Allodun of the 

 Upper Jurassic of the United States. 



The first discovery of the remains of Mesozoic mammals was 

 made in the Keuper or Upper Trias of the Rhastian Alps in 

 Bavaria. In 1847 Professor Pleininger of Stuttgart, while sifting 

 some sand from the Keuper of Diegerloch and Steinenbronn, 

 found, among an immense mass of teeth, scales, and unrecog- 

 nisable fragments of skeletons of fish and saurians, two minute 

 teeth, each with well- defined, enamelled, tuberculated crowns 

 and distinct roots, plainly showing their mammalian character. 

 These were considered by their discoverer to indicate a predaceous 

 and carnivorous animal of very small size, to which he gave the name 

 of Microlestes antiquus. Subsecpiently Mr. C. Moore discovered in a 

 bone bed of Rhaatic (topmost Trias) age, filling a fissure in the 

 Mountain Limestone at Holwell, near Frome in Somersetshire, 

 various isolated teeth with their crowns much worn, but apparently 

 including both upper and lower molars and a canine, which are 

 assigned by Sir R. Owen to Pleininger's genus Microlestes, and 

 described specifically as M. moorei. Under the name of Hypsi- 

 prymnopsis rhceticus, Professor Boyd Dawkins described a single tooth 

 with two roots discovered in the Rhaatic Marlstone at "Watchet in 

 Somersetshire. Sir R. Owen referred the latter tooth to Microlestes, 

 and if its describer is right in regarding it as a much worn premolar 

 of the type of those of Plagiaulax (Fig. 25) there would be evidence 

 that Microlestes was closely allied to the latter, from the molars 

 of which those of Microlestes are scarcely distinguishable. 



Plagiaulax, of the Dorsetshire Purbeck (Figs. 24, 25), is at once 

 distinguished from Tritylodon by its secant premolars, which, as already 

 mentioned, recall those of some of the Macropodidce, although readily 



