MARSUPIALS. 335 



nopsis Rhaeticus, from the Rhsetic deposits of Somersetshire, Eng- 

 land, and Dromatherium sylvestre, from the Chatham coal-fields of 

 North Carolina. Of less doubtful affinity are Tritylodon, from the 

 Triassic deposits of South Africa, and the numerous forms whose 

 fragments have been obtained from the British Oolites and the 

 island of Purbeck Amphitherium, Phascolotherium, Stereogna- 

 thus, Spalacotherium, Amblotherium, Stylodon, Triconodon, Tria- 

 canthodon, Plagiaulax and from the nearly equivalent deposits of 

 the Western United States (Diplocynodon, Stylacodon, Tinodon, 

 Triconodon, Dryolestes, Ctenacodon). Many, or most, of these 

 forms appear to depart to a certain extent from the normal type of 

 marsupial structure approximating the Insectivora hence, by 

 some naturalists, as Professor Marsh, they are relegated to distinct 

 groups Pantotheria and Allotheria supposed to have no living 

 representatives.* The Marsupialia are not represented in the Creta- 

 ceous deposits ; Meniscoessus, a form whose closest relationship 

 appears to be with the Jurassic Stereognathus, occurs (in associa- 

 tion with dinosaurian remains) in the Laramie formation of the 

 Western United States, the position of which in the geological 

 scale, as has already been intimated, is more properly with the 

 Cainozoic than with the Mesozoic series. 



The Tertiary marsupial remains of the Northern Hemisphere 

 belong principally to the earlier periods, beginning with the oldest 

 Eocene ; in Europe they have not been recognised higher than the 

 middle Miocene, and in North America, if we except the pygmy 

 opossum (Didelphys pygmsea) frbm the Miocene of Chalk Bluffs, 

 Colorado, no representative is known from deposits newer than the 

 Oligocene (White River beds). Barring the opossums,! whose 

 earliest remains have been found in the Eocene deposits of both 



* According to Professor Seeley, Ilvpsiprymnopsis, which appears to be 

 most intimately related to the modern kangaroo-rat (Ilypsiprymnus >, is founded 

 on the premolar toetli of Microlestes. The same authority recognises in Am- 

 pliithcriurn and Phascolotherium a strong combination of marsupial and in- 

 scctivore characters, and the indications of a "generalised insectivorous type, 

 modified from a monotreme stock in the direction of the marsupial plan " 

 (Phillips's "Manual of Geology," i., p. 520, 1*85). 



t Separated by some authors from the genus Didelphys as Peratherium 

 and Amphiperatherium ; Peratlicrium, whose range extends into the Miocene, 

 is represented by five or more species in the White River deposits of Colorado, 

 the largest of which about equals in size the mole (Scalops aquaticus). 



