206 U.S. NATIONAL MUSEUM BULLETIN 2 75 



mensal form, according to Schwarz and Schwarz, has evolved along 

 specific lines in response to its more intimate association with man 

 and normally has a longer tail (frequently longer than the length of 

 the head and body), a darker (more grayish) venter, richer (darker) 

 shades of color dorsally, a shorter face, and smaller molariform teeth. 

 In the wild form, the tail is shorter (always shorter than the length 

 of the head and body), the venter is white, rather than gray, and 

 forms a sharper contrast with the color of the pelage of the sides and 

 flanks. These authors contend that, in many areas, both indoor and 

 outdoor types of house mice are found. The outdoor (feral) types may 

 represent either wild or commensal types, which are less specialized 

 than the indoor types. 



The house mice of Libya, according to Schwarz and Schwarz, are 

 represented by two subspecies, M. m. praeiextus Brants and M. m. 

 brevirostris Waterhouse, representing, respectively, the wild and 

 commensal forms. 



Toschi (1954, pp. 264-265) summarized the work of all previous 

 workers on Libyan mammals and listed four subspecies of Mus mus- 

 culus as occurring in Libya. These included M. m. musculus, M. m. 

 brevirostris, M. m. gentilis (=M. m. praetextus), and M. m. orientalis. 

 Both M. m. gentilis and M. m. musculus were listed from Benghazi 

 and apparently represented, respectively, the feral and commensal 

 forms of M. musculus. These subspecies mentioned by Toschi were 

 based on specimens from widley scattered localities in Libya, and 

 many were assigned to a given subspecies without regard to distribu- 

 tional or taxonomic concepts. 



In the present study, many more specimens are available from 

 widely scattered localities in Libya, and two distinct color types are 

 discernible. Those from all interior localities represent the light-bellied 

 form and are white ventrally with the individual hairs white through- 

 out or plumbeous-colored basally. Dorsally, the coloration varies 

 from extremely pale individuals to quite dark-colored forms. In all 

 specimens from the interior of Libya, the dorsum and venter are 

 markedly contrasted in color. Specimens from the coastal plain near 

 Tocra in Cyrenaica typify the dark-bellied form in which the venter 

 is gray or brown and thus not contrasting with the color of the dorsum. 

 Light-bellied individuals also occur near Tocra but are less abundant. 



Setzer (1957) obtained both feral and commensal house mice in 

 Libya and was able easily to distinguish two types on the basis of 

 their dorsal and ventral coloration. He found, based on color, that 

 the commensal kind agreed with the description of the feral form 

 given by Schwarz and Schwarz, and that the feral kind agreed with 

 the description of the commensal form as given by the above authors. 

 He further stated that these color types did not represent subspecies 

 as understood by modern taxonomists. 



