HiN'i'ON — The Fossil Hare of the Ossiferous Fissures of Ightham. 237 



Lower Jaw. 



The lower jaws of both the fossil skulls described above from the Ightham 

 Fissure are preserved ; and they yield important evidence confirming the 

 reference of these remains to the L. variabilis group. (PI. XV., figs. 

 6 and 7.) 



Winge has pointed out that the molar teeth are somewhat more hypsodont 

 in L. ■variabilis than in L. europmus ;^ and a reference to the proportional 

 measurements recorded in Table IV. will show that correlated with this 

 greater hypsodonty there is an increase of all dimensions of lieight in the 

 lower jaw of the former group as compared with that of the latter. The 

 measurement " 5", which expresses the distance between the hinder edge of 

 the alveolus of the last molar and the hindermost point of the condylar 

 process, appears to be of some importance. With the exception of the higlily 

 modified L. var. grmnlandicus, this dimension appears to be constantly greater 

 iu L. variabilis than in L. eiiropceus, and its value increases in young indi- 

 viduals. The jaws from Ightham, which are adult, behave in this respect as 

 the recent young jaws. Again excepting L. var. groenlandicus, the diasteme 

 appears constantly if minutely shorter iu L. variabilis than in L. eiiropwtts. 



With regard to form, Woldrich- has stated that in L. variabilis the anterior 

 margin of the ascending ramus rises somewhat more steeply from the alveolar 

 border than in L. europxeus ; and Hilzheimer^ has added that in the latter 

 species the inferior margin of the ramus is usually straighter, and not so convex 

 as in the former. These characters appear to me to be fairly constant, but 

 the most diagnostic are those furnished by the proportions and by the 

 dentition described below. 



1 Winge, " Gronlands Pattedyr," p. 358 ; and Danmarks Fauna, "Pattedyr," p. 58. 



^ Woldrich, Sitzungsb d. k. Akad. d. Wien. math. nat. CI., Ixxxiv. Bd., 1 Abth., p. 222. The 

 measurements of the jaw from Zuzlawitz included in Table IV. are given in Woldrich's first paper : 

 ib., Ixxxii., Bd., 11 Abth., p. 16. 



^ HiLZHEIMER, op. cU., pp. 408-9. 



[Table IV. 



