60 THE GROWTH OF GROUPS 



longer than usual. The skull of a member of this family 

 group is shown in Fig. 3, together with a skull chosen as 

 representing the type of the parent species. 



This cranial type, however, was not an exclusive pos- 

 session of the group. The same type was occasionally 

 found in other places. It appears to be correlated with 

 large size. Whenever the head and body of a mole-rat 

 measures 200 mm. or more the skull is narrow in pro- 

 portion to its length, this is true without exception of 



G. bengalensis. Melanic sport. 



FIG. 3. 



specimens collected from various parts of India. A 

 large and relatively broad skull was never found. The 

 adult members of the group were of uncommon size, 

 being in that respect near to the highest limit found in 

 the species at large, hence, as usual, their skulls were 

 narrow. 



Let us re-state the case. I assume that there were a 

 group of at least thirty rats living in two adjacent houses 

 and possessing certain special characters, namely melanism 

 and a narrow type of skull, which seems to be associated 

 with bodily largeness. 



