240 Seientific Proceedings, Royal Duhlin Society, 



Dentition. 



TJlpper Incisors. — The front upper incisors of the L. variahilis group are 

 pretty constantly narrower than those of L. euro^M'us ; and they usually have 

 tlie longitudinal groove on the anterior surface deeper and narrower. 

 Forsyth Major' has pointed out that this groove has a more or less complete 

 filling of cement in the former group ; whilst in L. europcetis no trace of cement 

 is to be found in the incisor groove. To tliis rule there are, however, certain 

 exceptions. Thus Winge^ mentions a case of L. variabilis (var. glacialis, or 

 var. grcenJandicus) in which he could find no cement ; and Dr. Forsyth Major 

 tells me that lie has since seen a young specimen of L. europcetis which had a 

 little cement in the incisor groove. Occasionally the cement is present in 

 such force as to quite obliterate the incisor groove in L. variabilis.^ 



In both the fossil skulls from Ightham, described above, the anterior 

 upper incisors are narrow and have cement in their anterior grooves, and 

 similar characters are presented by all the detached examples from the 

 same place that I have seen. 



Correlated with the further extension backwards of its root the incisor 

 of L. variabilis is less strongly curved than that of L. europceus. This 

 straightening of the incisor is carried to the extreme in L. variabilis 

 grcenlandicits, in which form the tooth also is narrower than elsewhere.^ 



Nothing diagnostic is presented by the small posterior upper incisors. 



Lower Incisors. — The only difference observed is that the lower incisors of 

 L. variabilis are proportionally narrower and are straighter than those of 

 //. europceus. The fossil remains from Ightham agree with the other 

 members of the variabilis group in these respects. 



Cheek Teeth. 



The principal difference between the cheek teeth of the L. variabilis group 

 and those of L. europceus is that in the former they are a little more hypsodont 



1 Forsyth Major, "On Fossil and Recent Lagomorpha." Trans. Linn. Soc. Ser. ii. Zool., 

 vol. vii., p. 469. 



- WiNGE, " Gronlands Pattedyi-," p. 378. Hilzheimer states that he was unable to find any 

 cement in four out of eight skulls of L. variabilis examined by him ; but this is probably explained 

 by the confusion of the skulls of the two species to which I have already alluded : op. cit., p. 407. 



' This is the most likely explanation of the teeth mentioned by Woldrich. Sitzher. d. Ic. AJcad. 

 d. Wien. math.-nat. CI., Ixxxiv. Bd., 1 Abth., p. 221. 



* WiNGE regards these differences as specializations arising from differences in the food ; 

 " Fortsenderne bar den kun sjelden Lejlighed til at bruge til egenlig Gnavning of Bark o. s. v. 

 nsermest bruges de kun som Niptsenger til at afnippe Smaakviste og Blade ; de ere derfor 

 blevne spinklere," &c. "Gronlands Pattedyr," p. 358, 



