Acta Geologica 3. (1955)
4. szám - Kretzoi, M.: Dolomys and Ondatra
4* DOLOMYS AND ONDATRA 351 covering the fossa interpterygoidea in the primitive forms ; in the more advanced types, however, the squama becomes more and more eminent, gradually broadening out and finally reaching the lateral lamina that has remained in the higher level and, united with it, serves to extend the whole palatum durum. Among the above described forms, in the Microtus group a well characterised primitive palate with an oblique, flat squama can be observed in Pliomys episcopalis and Apistomys coronensis (with the difference of the palate being unusually broad), while three subsequent stages of the protruding and broadening of the squama are represented in Dolomys milleri and the forms of the genera Ondatra and Neofiber ; the stage of an elongated hard palate and a sharply cut-off hind palatal margin has been reached only in the Dolomys bogdanovi-marakovici group. As the stages of palatal development do not coincide with that based on the degree of observed general development (i. e. height of molar prisms etc.), it must be taken for a proof of the isolated evolution of each of the groups. To sum up the above, the forms of Dolomys may be divided into three natural groups : 1. Forms of small size with Microtus-like palatal development, very high dental prisms, simple wedge- or cap-shaped frontal prism of Ml5 and with a slight rib in the place of the second outer salient angle of M3. European faunae of the Sicilian age (save the most ancient ones) : Pliomys MÉHELY 1914 (Monotype : Pliomys episcopalis Méhely 1914). Species : episcopalis Méhely 1914, e. bolkayi (Kormos 1931), coronensis (Méhely 1914), lenki (Heller 1930), and the varieties of the latter (forma tenuis, depressa, intermedia, inflexa Heller 1930), and possibly hungaricus (Kormos 1934). 2. Forms of medium size (the living species resembling alpine snow-voles) provided with an extended posterior palatal margin, uniformly developed Mj-cap, M3 similar to that of Pliomys. In the Sicilian deposits of Dalmatia and living in the Dinarian Alps at altitudes up to and even exceeding 2000 m Dinaromys n. g. (Holotype : Microtus (Chionomys) marakovici Bolkay 1924). Forms that may be included : Dolomys bogdanovi (Martino 1922), marakovici (Bol kay 1924), grebenscikovi (Martino 1935), korabensis (Martino 1937), preni ensis (Martino 1940), dalmatinus (Kormos 1931) and, possibly, though it belongs probably rather to Pliomys, also Dolomys hungaricus (Kormos 1934). 3. Large-sized forms with well developed palatal squama ; hypsodonty of medium size, flat Mx cap, articulated, in young animals ; well developed ridge on the labial surface of M3 in the second salient angle. In the Calabrian and Sicilian deposits of Europe and North America : Dolomys Nehring 1898 (Monotype: D. milleri Nehring 1898). Included forms : D. milleri Nehring 1898, minor (Hibbard 1934), idahoensis (Hibbard 1934), monrupinus n. sp. These three groups are closely related to two living North American genera, viz. Ondatra (= Fiber) and Neofiber.