West- African Squirrels. 11 



for the sake of comparison ; it will be noticed that the tooth 

 of F. anerythrus agrees with that of F. pyrrhopus, and not 

 with that of F. mystax, which is the reverse of what might 

 have been expected, seeing that these two forms agree so 

 closely in external characters. 



It may be that this middle cusp is not so rare in existing 

 species as is generally supposed ; at any rate, it is a curious 

 fact that two squirrels which 1 have introduced to science — 

 the present one and F. Jacksoni from British East Africa — 

 have this character developed to a remarkable degree. The 

 latter species having far more cuspidate teeth the central 

 cusp is only strongly developed on the outer border, but the 

 extra fold of the enamel is well marked even in much-worn 

 teeth, giving the teeth a much more complicated appearance 

 than that found in any of its allies. A figure of the tooth 

 of this squirrel is also given of approximately the same age 

 (fig. 4), but owing to the strongly cuspidate nature of the tooth 

 it is difficult to do it justice in this manner of drawing. The 

 nature of the tooth will, however, be readily understood by 

 comparing this figure, which is only intended to show the 

 pattern, with the teeth of any of its allies or with the figure 

 of F. cepapi given by Dr. Major. The teeth of F. mystax, 

 on the contrary, with their evenly worn surface and clearly 

 laminated pattern, are exactly suited to this form of illustra- 

 tion. 



Both F. mystax and F. Jacksoni have undoubtedly very 

 near allies in their respective groups, whose teeth show no 

 sign of the middle cusp ; thus it would seem that no great 

 value can be attached to its presence or absence as a classi- 

 fying character. 



Alteration in the Arrangement of the Groups. 



Additions to the squirrels of the Faraxerus group of 

 Dr. Forsvth Major have caused me to look into the characters of 

 the species forming that subgenus. First I would mention 

 S. Nordhoffi, Duchaillu (?=& calliurus, Peters). The skull 

 of this squirrel has never been described ; in general form 

 and in the pattern of the molars it closely resembles 8. Stan- 

 geri from Fernando Po, but the size of the infraorbital foramina 

 is altogether unique among the Sciuridae, the openings being 

 4*5 millimetres high by 3 broad, and so approaching in size 

 within measurable distance those of Anomalurus. 



In connexion with the form of the infraorbital foramen, 

 another squirrel in the same collection must be mentioned : 

 this is IS. Wihoni, Duchaillu. Dr. Jentink, in his Mono- 



