24 EINAR LÖNNBERG, MAMMALS COLLECTED IN CENTRAL AFRICA. 



two outer and two inner, bnt their development is variable. Especially the posterior 

 inner eusp is often reduced in size, or even lacking. This is so irregular that the same 

 animal may have four cusps on one, but only three on the other side, and this may happen 

 in Iarge-toothed as well as in small-toothed specimens. 



The size of p x is variable as well. In the small-toothed female n:o 178 its greatest 

 transverse diameter is 8,5 mm. on one side, 8,8 mm. on the other; in the large-toothed 

 female n:o 160 it is resp. 9 and 9,2 mm.; in n:o 181 abont 9,8 mm., and in n:o 161 resp. 

 LO and 10,4 mm.; in the male n:o 70 the same dimension is 11,4 mm., and in the male 

 n:o 163 only 9,2 mm. 



The lower jaw is also extremely variable in shape. In the old male, 11:0 70, the 

 distance from the npper edge between both i r to the knob at the posterior margin of the 

 symphysis measures 41,2 mm. and in the other male, 11:0 163, 42,4 mm., but in thefemales 

 the difference can be greater as in the two large-toothed females, n:o 160 and 161, where 

 it is resp. 45 and 41,6 mm., and in the two small-toothed females resp. 40,3 and 39 mm. 

 The height of ramus horizontalis is in the others generally about 26 mm., or a little more, 

 but in the small-toothed 11:0 178 it is 28, and in the other small-toothed 11:0 224 only 

 22,4 mm. 



The variability extends, however, also to many other parts than those recorded in 

 the table, or mentioned above. 



Foramen magnum, is for instance in some specimens large, in others small, in some 

 oval, in others round (quite circular in 11:0 224), or even heart-shaped (11:0 178). In cor- 

 relation to the width of foramen magnum the breadth across condyli occipitales is verv 

 different in different specimens. It is smallest in the old male n:o 70 viz. 37 mm., and in 

 the large-toothed female n:o 161 viz. 37,4 mm. In the other male 11:0 163 it is 39 mm. 

 In the small-toothed females n:o 178 and 224 it is resp. 38,4 and 39,3 mm., and in the 

 large-toothed females 11:0 160 and 181 resp. 39,2 and 44 mm. 



Stränge to say variation with regard to supernumerary molars appears to be a less 

 rare occurrence among the Anthropoid Apes than could be expected. Bateson has in 

 his book »Materials for the Study of Variation» 1 recorded not less than four Chimpanzees 

 with supernumerary molars, which in three of the cases were situated in the upper, and 

 in one in the lower jaw. Among 8 full-grown Westafrican skulls now in the collections of 

 the R. Nat. Hist. Museum one has a quite small m* on the left side. The present author 

 has also at earlier opportunities seen supernumerary molars in Chimpanzee skulls from 

 Debundscha, Cameroon. In the series of 7 fully adult Chimpanzee skulls which Captain 

 Aruhenius has brought home from Rutshuru not less than 2 present such an anomalv, 

 viz. the numbers 160 (Pl. VI, fig. 3) and 178 (Pl. VI, fig 2). Both these are females, 

 and it is of interest to note that the former is large-toothed the latter comparativelv 

 small-toothed (conf. above). 



N:o 160 has a supernumerary molar as well in the uppcr as in the lower jaw. That 

 of the upper jaw is, however, more teratological as it is situated laterally of the molar 

 series outside of m' 1 of the left side, which has been pushed inwards a little but is of nor- 



1 London 1894. 



