334 Mr. G. Dollmaii en Arvicantliis abyssinicus 



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

 from tliose of T. kempiand T.fjrestoni: tlie smaller and much 

 more elongate atrium is truncate at the U[)per extremify, 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 VIIL 



fl^.=^atrium ; ;5. = peins; e;>. = epipliallum ; ^.z. = inferior flaprellum; 

 ^.s. = superior ila.r>-ellum ; y.c. = calcareous gland; c.d. = \Qa deferens ; 

 i.e. = bursa copulatrix ; v. = vagina. 

 The fractions sliow the enlargements of the drawings. 



Figs. 1, 2. Urocyclus siynatus. 

 Figs. 3, 4. Trichoto.ron ketiieyisis. 

 Figs. 5, 6, 7. Trichoto.von kemin. 

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



XLII. — On Arvicantliis abyssinicus and allied East-African 

 Species, icith Descriptions of Four neiv 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 Arvicantliis ahi/ssinicus group. 

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

 in individuals of the same species, the subject presents so 

 many difficulties that this paper cannot be looked upon as 

 more than a temporary scheme for the arrangement and 

 classification of the several torms. The key appended below 

 is largely founded on skin characters and general dimensions, 

 as these appear the most satisfactory. Altogether some four 

 hundred 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 

 longt-r than length ot head and body. 

 o. Light underpartsuot sharplv marked oti* 

 from Hanks. 

 a\ Size of body large, about loO mm. 

 in length. General colour pale 

 sandy ochraceous mixed with black. 

 (Egyptian Soudan.) (I) (csticulans. Sund. 



