CRICETUS 601 



narrowly and equally rounded. Molar rows about half as long as 



diastema in fully adult skulls, relatively longer in immature 



individuals ; anteriorly the rows diverge noticeably, owing to 



somewhat oblique position of wi\ so that length of tooth-row is 



only equal to greatest width of palate and alveolus of one side. 



Anterior upper molar with four or sometimes five roots and six 



tubercles, its crown about as large as m"^ and first pair of 



tubercles of m^ ; the two anterior slightly smaller than the 



others ; outer tubercles in line with each other and parallel to 



main axis of crown, antero-internal tubercle somewhat displaced 



outward so that the line of the three inner tubercles curves 



outward in front, adding to the oblique appearance of the tooth ; 



a deep pit in median line between each pair of tubercles, the pits 



at a certain stage of wear assuming the form of enamel islands, 



or of re-entrant loops extending obliquely backward from base of 



outer tubercles and later disappearing ; at the stage in which the 



pits have become loops the crown of the tooth has an enamel 



pattern consisting of six triangles arranged in opposite pairs but 



nearly closed by the backward extension of the outer re-entrant 



angles ; at the later stage when the last trace of the pits has 



disappeared, the bases of the triangles open broadly into each 



other, forming three transverse loops nearly divided by the equal 



external and internal re-entrant angles. Second upper molar 



4-rooted, the crown with four tubercles resembling the posterior 



four tubercles of first ; anterior border of crown with narrow 



transverse ridge, best developed on outer side though scarcely 



rising above level of extreme base of anterior tubercles. Third 



upper molar 3-rooted, slightly more than half as large as second, 



the two anterior tubercles normal in form though slightly reduced 



in size, the two posterior tubercles small and confluent, the outer 



more reduced than the inner, but traces of all the elements of 



the tooth present ; anterior ridge well developed on outer side of 



middle but obsolete or absent on inner side. Mandibular molars 



resembling the corresponding upper teeth in general form and 



structure, but m, i^elatively smaller and iiig relatively larger, 



the tubercles slightly but evidently alternating, the inner more 



anterior in position than the outer, and deepest re-entrant angles 



on inner side instead of on outer side, the inner extremities of 



the angles at no stage so distinctly isolated as pits. First lower 



molar at all ages with six nearly closed triangles, distorted in 



unworn teeth by the cusp-like elevation of their outer walls ; 



anterior pair of cusps noticeably smaller than the others but 



essentially in line. Second and third lower molars like posterior 



four cusps of first, the crown of m^ nearly as large as that of nh,, 



its posterior pair of cusps very little reduced ; anterior border of 



each tooth with low but evident ridge on outer side. 



RemarJcs.—Cricetus cricetus difi:ers conspicuously from all 

 other European rodents in its unusual colour pattern with 

 under parts entirely black. Four local forms have been described. 



