42 On Microclioerus erinaceus (Wood). 



two premolars (pm 3—4) are semi-procumbent and single- 

 rooted, the last premolar has in addition an internal cone and 

 a second root. There is a gradual increase in size, the last 

 tooth having an antero-posteiior diameter of 3 mm. 



The first two molars are equal in size, 8'5 mm. in length 

 and 3 mm. across; the first has a distinct paraconid, which is 

 lost in the following teeth. The last molar has an enlarged 

 talon and third root. 



In all the lower teeth the external cingulum is well marked 

 and the molars show the same tendency to secondary wrinkles 

 as the upper ones. 



As I have stated above, the precise position of this form is 

 as yet obscure, as is the case with so many of the primitive 

 Eocene Primates and Insectivores. Wood, the describer of 

 the type, placed Microchoerus with Hyracotherium, to which 

 form it has only the very slightest and most superficial 

 resemblance ; but that he was rather doubtful of its true 

 nature appears, as Lydekker has pointed out, in the specific 

 name given to it. Lydekker himself claims it as one of the 

 Erinaceidge and as allied to Hyopsodus, but Matthew has now 

 shown that the latter belongs to a group of Insectivores well 

 defined from Erinaceus, and Schlosser further gives his 

 opinion against any affinity between Microchoerus and Erina- 

 ceus. The latter author considers it to be allied to Hyopsodus 

 and Pelycodus, the latter a Primate, while the former is an 

 Insectivore, as both Matthew and Wortman have shown. 



Microchoerus differs from Hyopsodus in several particulars ; 

 the tooth-formula is ^l'^ or 2 '\\ '% against g'|'^ . In the 

 latter form none of the anterior teeth are enlarged, the pre- 

 molars have a more distinctly pronounced talon, and the upper 

 molars are without the mesostyle. 



Wortman suggests an alliance with Necrolemur, and the 

 general shape of the lower jaw and the tooth-formula, even 

 to the small and vestigial second tooth, shows a striking 

 resemblance. The only difference is the absence of the meso- 

 style in the upper molars in Necrolemur. On the whole, 

 with the material at command, it seems best to regard these 

 two forms as the nearest relations hitherto known. 



References. 



Wood. — London Geological Journal. 1845. 

 Lydekker. — Quart. Jo urn. Geol. Soc. xli. 1885. 

 Schlosser. — Beit. z. Pal. Oest.-Ung. 1887. 

 Wortman. — Amer. Journ. Sci. xv. 1908. 

 Matthew. — Mem. Amer. Mus. Nat. Hist. ix. part 6. 



