Boros István (szerk.): A Magyar Természettudományi Múzeum évkönyve 3. (Budapest 1953)
Éhik, Gy.: The occurrence of the Root-vole (Microtus oeconomus Pall.) at the Kisbalaton
contact the former biotops now under water. Even so, oeconomus was undoubtedly a rarity in the same places where it had been formerly common. I wish to say only that 1951 was an oeconomus-poor year. It is a characteristic data for the 1950 abundancy of oeconomus that, along the Heviz Canal on a reach of some 1750 steps, I got 40 various animals, among them 6 oeconomus, with 100 traps. A still better result was had in the reed jungle west of the island Diás on a 200 steps line, where I worked with 20 live-animal snares during 5 days, getting 1 or 2 oeconomus every day. As regards age I caught only adult specimens in June, with a mixed result in July and September. Most young animals were trapped in September. Of all collected animals' I give only the data of intact crania or of very slightly injured ones. By the way of introduction I wish to establish the fact that the Kisbalaton animals belong to the subspecies M. oeconomus mehelyi. Since the description of this subspecies (2) was made based on a few animals and on a single intact cranium only, the results of my recent examinations complete the original description and my former' conclusions. The-color of the Kisbalaton specimens is, in -toto, somewhat darker than those of the Somorja specimens. The dark dorsal streak is broader, the lateral coloration less yellowish but of a more expressed chestnut hue. My single german specimen is also of a chestnut color with a stronger grey shade. It is very striking that the fur of both the Somorja and the Kisbalaton specimens are exceedingly long, lustrous, and silky fine. I have seen similar furs in animals of the far north only. This very rich fur seems to be the result of a very wet and humid biotop. The darker hue of the Kisbalaton specimens may also be in connection with the special biotop, but I cannot find this fact satisfactory enough to separate the Kisbalaton animals from the Somorja specimens. I could weigh two animals only in 1951 ; the two male specimens measuring 40 grs and 50 grs. The data of this latter (Coll. nr. 29) are given in the Table ; the former came in a very injured state into my hands. The dentition of the Kisbalaton oeconomus varies somewhat. So, for instance, the depth of the re-entrant .angles along the aboral lingual part of the anterior loop in m v causing the eventual occurrence of a separate triangle of the posterior lingual aboral loop by the meeting of the enamel ridges ; appearing thereby as à separate third internal triangle though it is nothing else than a curiously modified part of the anterior loop. Even the oral part of the anterior loop varies ; its lingual part is sometimes very smooth, almost resembling that of nivalis, but more often it is divided into two parts by a re-entrant angle, the ratio of which is also exceedingly changing. Similarly to the lower m lf the terminal loop of the upper m 3 varies also, to which the parts beyond the first lingual and second inguinal triangles belong. The ridged and angular crania of oeconomus mehelyi are very striking. This was also mentioned by Zimmermann (5), who said : »Der einzige vollständige Schädel übertrifft an Grösse und Kantenbildung alle mir von oec. ratticeps vorliegenden« (p. 180). In my craniometric measurements I did not take into consideration the younger animals of 26,6 mm, or even smaller, condylobasal length. I consider as semiadult animals specimens which have a condylobasal length of 26, 3—26,9 mm ; having estimated as really adult animals those only which exceed these figures. Again, very old specimens are separated of the others by the designation »sen«. (senex). Let us take now the condylobasal length : 26,3 mm 26,6 mm 27,1 mm 27,6 mm 28,1 mm 28,6 mm 29,1 mm 29,6 mm 26,5 27 27,5 28 28,5 29 29,5 30 4 sp. s 8 7 7 1 4 2 - 2
