LEMMUS 189 



they become rather closely approximated, and then more slowly 

 diverge again to their junctions with the occipital crest. The 

 ridges are situated throughout the greater part of their course 

 upon the upper edges of the squamosals; as the ridges become 

 more and more approximated throughout their course with 

 advancing age the squamosals encroach progressively and at a 

 corresponding rate upon the frontals, parietals, and interparietal ; 

 in old age the squamosals are separated in front by only a very 

 small interval, and the posterior or intertemporal breadth of the 

 frontals and the area of the dorsal surface occupied by the 

 parietals and interparietal are very greatly reduced. Squamosals 



Fig. 77. — Lcmmus lemraus Linnaeus. 



Cheek-teeth (crown views) : a. right upper, h. left lower molars arranged 



and lettered to show the homologies of the cusps. Recent. 



c. Left lower molars of a fossil jaw from the Doneraile Cave, Co. Cork, 



Ireland. Pleistocene. 



anteriorly forming large post-orbital crests which form the 

 somewhat squared shoulders of the braincase ; posteriorly their 

 Bupratympanic portions are very short and broad ; supra- 

 tympanic fenestra on each side very small and more forwardly 

 placed than in voles. Lambdoid crest very salient laterally and 

 formed chiefly by the hinder edge of the supratympanic portions 

 of the squamosals, the lateral processes of the supraoccipital 

 being very short. Occiput rather low and depressed, somewhat 

 oblique in old age, with strongly developed median and lateral 

 crests. 



In ventral view the rostrum is conspicuously longer than in 

 Synapto7)tys and JMyopiiit, its greater length being due to the 

 relatively larger incisors; in the two genera just named the 

 diastema is barely equal to or even less than the length of the 



