40 BULLETIN 99, UNITED STATES NATIONAL MUSEUM. 



On account of its large size I have referred this specimen to Imidei, 

 although I quite agree with Doctor Lonnberg's statement that ''it 

 appears hardly possible to maintain L. i. Mndei as a subspecies as it 

 only differs in size,"^ and the specimen recorded by Mm from the 

 Mau Escarpment (the tjipe region of iheanus) exceeds in cranial 

 dimensions the type of hindei. The large masseteric knob which has 

 been given as a specific character of ibeanus is characteristic of the 

 old male, and is wanting in young adult male and adult female 

 skulls in our collection. Sufficiently large series of skulls of LopMomys 

 to work out the ordinary individual variation and the increase in size 

 with age are greatly desired. 



Family EHIZOMYID^. 



Genus TACHYORYCTES Ruppell. 



[1835.] Tachyoryctes Ruppell, Neue Wirbelth. Fauna Abyssinien gehorig. Saug., 



p. 35. 1835-1840. ( T. splendens.) 

 1843. Chrysomys Gray, List Mamm. Britisli Museum, p. 150. (T. splendens.) 



The United States National Museum collection contains eight 

 forms of the East African mole-rat. While these are all closely 

 related species, all have constant characters of differentiation, and 

 intergradation between any two of them is not indicated by this ma- 

 terial. There is in no case any doubt as to where any given specimen 

 should be listed. When collections have been made over all parts 

 of British East Africa and Abyssinia numerous forms will doubtlessly 

 be connected by complete chains of intergrades and the final mono- 

 grapher of the genus will be obliged to reduce many of the named 

 forms to the rank of subspecies. Six currently recognized forms are 

 not represented in our collection. These are splendens Ruppell, 1835, 

 and macrocepJialus Ruppell, 1845, from Abyssmia; annectens Thomas, 

 1891, doubtfully from Ijake Naivasha; hadius and storeyi Thomas, 

 1909, from Eldoma Ravine and Lake Elmenteita, British East Africa; 

 and somalicus Osgood, 1910, from Somaliland. The species described 

 by Thomas in 1891, annectens, is larger than any form in our collection 

 excepting rex of Mount Kenia; its type locality seems to be in question, 

 but the specimen on which the name is based is supjDosed to have been 

 collected somewhere in the vicinity of Lake Naivasha. All of our 

 specimens from Lake Naivasha belong to a much smaller species 

 described by Thomas in 1909 from the same region. 



The examination of large series of specimens of Tachyorctes proves 

 the utter lack of value of certain skull characters which have ordi- 

 narily been used in diagnosing new species. The shape of the nasal 

 bones, for example, is so variable that skulls in almost any series 

 exhibit the entire range of variation usual in the genus. The presence 



» Kungl. Sv. Vet. Akad. Handl., vol. 48, No. 5, p. 101. 1912. 



