334 Mr. G. Dollman on Arvicantliis abyssinicus 



The reproductive organ (fig. 3) is also very different 

 from those of T. kempi and T. prestoni'. the smaller and much 

 more elongate atrium is truncate at the upper extremity, the 

 penis is much longer and more pitted, and the lower flagellum 

 is much shorter, the bursa copulatrix is ovoid. I found four 

 darts, relatively rather large, more recurved, and of a some- 

 what club-shaped form. 



EXPLANATION OF PLATE VIII. 



fl?. — atrium; ;?. = penis; e^;. = epiphallum ; ^.t. = inferior flapellum; 

 Ji.s. = superior liagellum ; ffl.c. = calcareous giaud ; c.d. = vas deferens ; 

 i.e. = bursa copulatrix; z'.= vagina. 

 The fractious show the enlargements of the drawings. 



Figs. 1, 2. Urocyclus si[/natus. 

 Figs. 3, 4. Trichotoxon keniensis. 

 Figs. 5, 6, 7. Trichotoxon kefnjn. 

 Figs. 8, 9, 10, II. Trichotoxon prestoni. 



XLII. — On Arvicanthis abyssinicus and allied East-African 

 Species, tvith Descriptions of Four iiew Forms. By GUY 

 Dollman. 



(Published by permission of the Trustees of the British Museum.) 



The following paper is an attempt to arrange in systematic 

 order the various species and subspecies of East-African 

 field-rats belonging to the Arvicanthis ahyssinicus group. 

 On account of the great variation in colour and size met with 

 in individuals of tlie same species, the subject presents so 

 many difiiculties that this paper cannot be looked upon as 

 more than a temporary scheme for the arrangement and 

 classification of the several forms. The key appended below 

 is largely founded on skin characters and general dimensions, 

 as these appear the most satisfactory. Altogether some four 

 Iiundred specimens have been examined, and as far as possible 

 average dimensions for each species and subspecies are given. 



Key to the Species and Subspecies. 



A. Tail approximately equal to or rather 

 longer than length of head and body. 

 a. Light underpartsnot sharply marked off 

 from flanks. 

 a^. Size of body large, about 150 mm. 

 in length. General colour pale 

 sandy ochraceous mixed with black. 

 (Egyptian Soudan.) (1) testicularis, Sund. 



