the O'enus Otomys. 267 



Section I. 



Tlic forms in this Section, as will be seen from the key (A. a^), 

 arc characterized by the smooth lower incisors and, in most 

 cases, the modification of the anterior two laminae of nii. The 

 exact structure of the molars of Otomys has never, I believe, 

 been worked out. It is not, therefore, certain whether the 

 nuxlified portion of ?>«, in this Section represents one or two 

 lauiinie; but in view of the almost universal presence of four 

 laminae in/z/j throughout the rest of the genus, and the fact that 

 Sloyyettiy which undoubtedly belongs to this Section, has four 

 complete laminae in that tooth, I have accepted the proba- 

 bility that the modified area represents two laminae. This 

 modification takes two forms, which, in well-marked cases, 

 are quite distinct and cannot have been produced the one 

 from the other by wear. In both forms the inner ends of 

 the two anterior lamintc are produced in a curve, the ante- 

 rior backward and the posterior forwards, and fused into one 

 continuous strip of enamel in the shape of a horseshoe with 

 the open end outwards. In w hat I have called the " kidney "- 

 shaped form the two free ends of the horseshoe arc doubled 

 inwards, showing a heart-shaped or kidney-shaped pattern; 

 in the " spiral ""^ form the free end of the posterior lamina is 

 not or scarcely })rodueed, while that of the anterior is 

 produced boldly inwards and again doubled on itself, thus 

 showing a distinct spiral pattern. 



These forms of modification, though one form is found 

 in a large majority of individuals of a given species or 

 subspecies, are not quite constant, and I have therefore not 

 relied upon them in my key. 



(1) Otomys Brantsi. 



Euryotis Brantsi, A. Smith, 111. S. Afr. Zool. 1839, pi. xxiv. 

 Euryotis pallida, Wagner, Wiegm. Arch. Naturg. 1841, p. 13J. 

 Otoniys nijifrons, Itiippell, Verzeichn. Mus. Seuck. i. 1842, p. 28 (noni. 

 nud.) ; Wagner, iSchreb. Saug., Suppl. iii. 1843, p. 507. 



158 a (41.803). Mouth of Orange Hiver (skull 70^ c) 

 {A. Smith, type). 



764 6 (no skin). S. Africa {A. Smith), 



98. 9.6. 1 (in. al.). Namaqualand. (Cape Town Museum.) 



4.2.3.81-88. Klipfoutein &c., Namaqualaud. (Rudd 

 Exploration.) 



The type is very young and immature, and although it 

 seems in some respects to resemble suspiciously the eastern 

 form, still, all things considered, I am constrained to agree 

 with and follow Thomas (P. Z. S. 1901, vol. i. p. 178) in 



