﻿362 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



20.0), 19.6 (18.1-21.4) ; length of anterior palatal foramina 7.4 (6.8- 

 8.3), 7.6 (7.0-8.3) ; alveolar length of upper molar series 6.8 (6.3-7.2) , 

 6.9 (6.5-7.8); least interorbital width 6.1 (5.8-6.3), 6.1 (5.6-6.6); 

 length of nasals 14.9 (13.5-15.8), 15.2 (13.3-17.0). 



Remarks. — If one were to recognize subspecies of the commensal rat 

 then the three color types mentioned under description would become 

 (1) Rattu.3 rattus rattus., (2) Rattus rattus alexandrinits (which may 

 be considered topotypical), and (3) Rattus rattus frugivorous. How- 

 ever, since the three basic color types do not appear to segregate out in 

 any given series from any given locality as just these three color types, 

 but show in six of thirty-four specimens intermediate conditions be- 

 tween any two of the three, it is felt that here, as in Acomys, is an ex- 

 pression of some genetic factor, called by some a single gene character 

 for melanism. Certainly, one of the criteria for subspecies is a free 

 interbreeding between two or more contiguous kinds which would be 

 expected to produce intermediate types. It is extremely hard, though, 

 to visualize three distinct subspecies occupying the same environmental 

 niche. Flower (1932, p. 409) and many others mention the fact that 

 no habitat differences could be ascertained between the so-called three 

 subspecies. It may be that if these animals were to be found ferally, 

 one or the other of the three types would segregate and be com- 

 pletely recognizable. It is worthy of mention, though, that the four 

 wild-caught animals from 5 miles west of Simbillawein show all 

 three color types plus one that is intermediate between types two and 

 three. 



It is felt that, since there appears to be no segregation, so far as is 

 known, it is best to ignore the subspecific names for the three above- 

 mentioned rats until such time as these names can be shown to be valid. 



MUS MUSCULUS Linnaeus 

 Mus musculus Linnaeus, Systema naturae, ed. 10, p. 62, 1758 (Upsala, Sweden). 



Specimens examined. — Eighteen. Behera Province : Alexandria, 6 ; 

 ^2 mile west of Dikheila Airfield, 1 ; Heliopolis, 1 ; Maadi, 1. Daqahlia 

 Province: 5 miles west of Simbillawein, 3. Giza Province: Kafr 

 Taharmes, 1 ; Kuniessa, 1 ; Talbia, 1. Suez Canal Zone : Port Said, 1 ; 

 Suez, 2. 



Description. — Three color phases are present in the small series 

 from Egypt. They are: (1) Pallid Neutral Gray rather strongly in- 

 termixed with black; (2) Cinnamon-Brown without so much black 

 intermixed; and (3) Mummy Brown, strongly suffused with black. 

 In all color phases the hands and feet are white ; the bellies in the first 

 two phases are white ; in the first the hairs are white to the bases, in 

 the second the hairs are plumbeous at the base; in the third phase 

 the belly is buffy, with the hairs plumbeous at the base. In all three 



