460 Mr. M. A. C. Hinton on the 



(2) M. orcadensis orcadensis, Millais. 

 Hab. Pomona. 



(3) M. orcadensis rousaiensis, subsp. n. 



Hub. Rousay. 



Type. An adult male (B.M. 12. 7. 5. 7). 



Diagnosis. — External appearance as in M. o. orcadensis. (Collector's 

 measurements of type : head and body 135 mm. ; tail 36 ; hind foot 18 ; 

 ear 12.) Skull with short and broad brain-case, as in o. orcadensis and 

 o. sandayensis, occasionally depressed ; anterior approximation of squa- 

 mosals and saliency of their postorbital crests intermediate between 

 o. orcadensis and o. sandayensis ; interparietal and supratympanic fossse 

 essentially as in o. orcadensis ; jugal always slender, as in o. sandayensis ; 

 c ..t. l always with deep outer fold, as in o. orcadensis. (Cranial measure- 

 ments of type : condylo-basal length 28*9 mm. ; zygomatic breadth 17*6 ; 

 interorbital constriction 3 - 7 ; occipital breadth 12*7; occipital depth 7'0; 

 nasals 8 - 9 ; diastema 8 - 9 ; maxillary cheek-teeth (alveolar) 6 - 7 ; man- 

 dible 18*8 ; mandibular cheek-teeth (alveolar) 0*7.) 



(4) M. orcalensis xoestrm, Miller. 

 Hab. Westray. 



(5) M. orcadensis sandayensis, Millais. 

 Hab. Sunday. 



M. sarnius, Miller, from Guernsey, Channel Islands, is a 

 near relative of M. orcadensis. It is distinguished by its 

 external appearance, which recalls the agrestis group, and by 

 its longer and narrower brain-case, less spreading zygomata, 

 shorter nasals and diastema, rather longer molars, and 

 smaller bullae. The nasals are cleft by a small process of the 

 frontals, as in orcadensis, but the median septum of the 

 hinder palate is not grooved. Both portions of the temporal 

 muscle appear to be considerably weaker than in orcadensis, 

 and consequently the adult skull differs far less from the 

 young. The distance between the temporal ridges behind is 

 relatively greater in adult sarnius than in any stage examined 

 in any Orcadian form ; the interparietal is therefore scarcely 

 modified, and the supratympanic fossae are not more extensive 

 than in young sandayensis. Anteriorly the squamosals are 

 widely separated, but the posterior process of the frontals 

 tends to become narrow with age. The jugal is light ; the 

 fourth outer fold of ^73 is well developed. The occiput is 

 intermediate in depth between those of orcadensis and 

 sandayensis. 



