On Microchoerus erinaceus ( Wood) . 39 



retain their curvature and thick enamel and form a more or 

 less well-marked accessory or vestigial inner angulation 

 behind ; third or antero-external prism of last lower molar 

 less reduced than in D. henseli, and there is frequently a more 

 or less well-marked minute fourth outer vestigial angulation. 



Measurements. — Langwirh Cave skull : breadth of rostrum 

 7 # mm. ; length of nasal 9*5 (ca.) ; diasteme 9"6 ; molar 

 series (alveolar) 8 3. 



Remarks. — The maxillary teeth of the skull figured by 

 Sanford from the Somerset caves (Q. J. G. S. xxvi. pi. viii. 

 figs. 4 & 4 a) agree witli those of the species here described 

 and with D. torquatus. There is every reason to suppose 

 that the lower jaw from the same place figured by Sanford 

 (loc. cit. figs. 2 & 2b), and to which he gave the name of 

 M Arvicola " gulielmi, belongs to the same species of Dicro- 

 stonyx as does the skull, despite the abnormal appearance of 

 the last lower molar ; and therefore, unless it can be shown 

 that the lower jaw does come from a different species, the 

 name of "gulielmi" must be used for this species. 



D. gulielmi is distinguished from I), torquatus, with which 

 it agrees in tooth form, by its considerably larger size, shorter 

 and broader incisive foramina, broader nasals, and much 

 heavier teeth. Dr. Forsyth Major as long ago as 1872* 

 called attention to the dental differences in the fossil forms and 

 suggested that there were two species of Dicrostonyx in the 

 Pleistocene deposits of Western Europe, and it affords me 

 great pleasure to be able to support the suggestion by 

 establishing it as a fact. 



V. — Microchoerus erinaceus {Wood). By C. FORSTER- 

 COOPER, M.A., F.Z.S., Trinity College, Cambridge, 

 University Demonstrator in Animal Morphology. 



[Plate m.] 



This revision of the interesting little form Microchoerus 

 erinaceus is the result of an examination of the specimens 

 contained in the collection of the British Museum (Natural 

 History) and in that of the Sedgwick Museum at Cambridge. 

 I am indebted to Dr. A. Smith Woodward, F.R.S., and to 

 Professor T. McKenny Hughes, F.R.S., for permission to 

 study the specimens in their collections. 



* Forsyth Major, Atti di Soc. Ital. di Scienz. Natur. xy. p. 123 (1872). 



