CKICETUS 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 m 1 , 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 2 and first pair of 

 tubercles of m 3 ; 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 1 relatively smaller and m 3 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 ro 3 nearly as large as that of m 2 , 

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

 each tooth with low but evident ridge on outer side. 



Remarks. — Gricetus cricetus differs conspicuously from all 

 other European rodents in its unusual colour pattern with 

 underparts entirely black. Four local forms have been described. 



