404 Mr. O. Thomas on 



of appendages in secondary symmetry. On the other hand, 

 the lew cases of " double limbs " recorded by Bateson in 

 Arthropods (as well as those recorded since^ e. g. by Zeleny, 

 Biol. Bull. ix. 1905, p. 152) have the two parts in symmetiy 

 with each other. Bateson discusses the possibility of " such 

 a phenomenon as the representation of one of the appendages 

 by two identical appendages standing in succession/' and 

 concludes that it is " probably unknown and perhaps against 

 Nature'' ('Materials for the Study of Variation/ 1894, 

 p. 539). It would seem, nevertheless, that the specimen 

 now described presents an instance of this very phenomenon, 

 for the extra segments springing from what is morphologi- 

 cally the antero-ventral surface of the left chelip.ed are them- 

 selves unmistakably parts of a left cheliped. 



XLVI. — New Forms o/ Akodon and Phyllotis, and a neio 

 Genus for " Akodon " teguina. By Oldpield Thomas. 



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



Akodo7i mollis altorum, subsp. n. 



The common olive-coloured Akodon of the Ecuadorean 

 Andes. 



Essential cliavacters as in true mollis^ but the fur longer 

 and the colour much darker. Upper surface approximating 

 to Ridgway's "olive/' while in true mollis. \i is between 

 wood-brown and broccoli-brown. Under surface greyish, 

 washed with dull buffy. Hands and feet greyish, darker than 

 in mollis. Tail averaging a little shorter than in mollis, 

 blackish above, dull greyish white below. 



Skull and teeth as in true mollis. 



Dimensions of the type (measured in flesh) : — 



Head and body 110 mm. ; tail 70; hind foot 22 ; ear 16. 



Skull : greatest length 28 ; condylo-incisive length 26 ; 

 interorbital breadth 4*7 ; palatal foramina 6*7 ; upper molar 

 series 4*3. 



Hah. Ecuadorean Andes from Quito southwards into Peru. 

 Type from Canar. Alt. 2600 m. 



Type. Adult male. B.M. no. 99. 9. 9. 99. Original num- 

 ber 252. Collected 8th April, 1899, by P. O. Simons. 

 Presented by Oldfield Thomas. 



An examination of the fine series of Akodons obtained in 



