the Genus Otoinys. 265 



north of tlie Equator, while the irroratus group inhabits the 

 whole eastern liall" ol" the continent from Cape Town to the 

 Equator, the forms south ol" the Zambesi showing normally 

 six lamina; in m\ with about 5 per cent, of exceptional 

 inclividiuiLs having seven lamituc, while those north of that 

 river show exactly the reverse. The western half of Africa 

 is unfortunately unrepresented in the collection, so far as 

 Section II. is concerned, except by a single specimen from 

 Angola and a skull from the Cameroons, both showing seven 

 laminic in iii'. This would seem to show that the rule of 

 seven lamin;x) in m'' in the northern forms holds good also of 

 the west coast. But the Angola specimen probably reached 

 that country via the Congo Valley (the common Otomys 

 of Angola seems to be the aberrant Anchietce of Bocage), and 

 therefore is no indication of the truly indigenous fauna of 

 western Soutii Africa. 



I arrange the forms I have been able to distinguish in a 

 key as follows : — 



Key. 



A. wj, composed of four lamina3 or llieir 

 equivalents. 

 a\ Lower incisors not or very fiiiiitl}' grooved. 

 a^. ?«■' composed of two complete laminas 

 aud a modified posterior portion. 

 ]Jull;e large (11 mm.). 

 «'. Tail long, | of head aud body ; hind 

 foot 28 mm. ; lower incisors with a 

 faint groove ; length of upper molar 

 series* 8 mm. (Namaqualand.) .. (1) Braidsi, Sm.. 

 b^. Tail shorter, little more than i as 

 long as head and body ; hind foot 

 25 mm. ; lower incisors smooth j 

 length of upper molar series 7 mm. 



(Deelfontein, C.C.) (-) ^- hUeolus, Thos. Sc 



b"^. m^ composed of three complete laminas [Schw. 



and a modified posterior portion in the 

 shape of a trefoil. 

 a^. Two anterior laminte of m^ mudified 

 and showing a " spiral " or " kidney- 

 shaped " pattern ; tail long, stout, 

 black, 

 a*. Grooves of upper incisors distinct. 

 a'. Larger; head aud body 175 mm. ; 

 tail shorter, 90 mm. ; ears 



* The length of the upper molar series is a very difficult measurement 

 to take in this genus, owung to the sloping laminae which constitute the 

 crown of each tooth. I have here and throughout this paper used a 

 measurement from the posterior point of the crowu to the base of the 

 enamel on the front of the anterior tooth. 



