E. T. Newton — SpermopMlus beneath Boulder-Clay. 53 



anterior clieek-teetli, yet these are not sufficiently marked to enable 

 one to separate the species. On the whole these fossil teeth would 

 seem to agree best with those of S. citillus and S. Altaicas (=z S. 

 Eversmannii). And judging from the measurements of the teeth of 

 these two species given by Dr. Nehring (Neuen Jahrbuch, 1880, 

 Band II. p. 121), and of those in the British Museum, our fossils 

 agree best with the S. Altaicus ; for the three teeth preserved are as 

 long as the four in S. citillus, that is, 8'5 mm., while the length 

 occupied by the four when complete must have been as nearly as 

 possible the same as in the S. Altaicus, that is, 11*5 mm. It will be 

 noticed that these measurements are much less than those given 

 by Dr. Falconer for his *S^. erythrogenoides, which was 0*52 in. or 

 13*4 mm. 



Dr. Nehring sems to think (loc. cit.) that Dr. Falconer's species is 

 very closely allied to the S. Altaicus, if not the same ; but the measure- 

 ments are certainly much greater than in the latter species. 



With regard to the upper teeth, the recent S. Altaicus has the 

 second, third, and fourth cheek-teeth proportionately wider from 

 before backwarks than in either of the other species, and this is due 

 to the somewhat greater development of the hinder depressed space 

 and its inclosing ridge. The second upper (pm. 4), as in other 

 species, is a little smaller than the third or fourth (m. 1 m. 2). The 

 pair of fossil teeth would agree in form with either of these three 

 teeth, as they have the hinder depressed space developed to about 

 the same extent, and consequently the antero-posterior measurement 

 of the crown bears about the same proportion to the rest of the 

 tooth. But in size they agree best with the fourth tooth (m. 2), 

 being rather larger than the anterior teeth. The last upper tooth in 

 the recent specimen has the hinder space much enlarged, so as to 

 form a heel, and thus gives the tooth a greater antero-posterior extent. 



The SpermopMlus citillus has the second upper tooth (pm. 4) of 

 about the same proportions as it has in S. Altaicus, but the third and 

 fourth teeth are narrower from before backwards. The fossil teeth 

 are larger than either of these, and seem to me to differ from the 

 second and third, which are most near them in size in the larger 

 development of the hinder space. 



The only American SpermopMlus which I have had the opportu- 

 nity of examining was the S. lateralis, and this had the upper teeth 

 of a different pattern, and quite unlike the European forms, or this 

 fossil. 



Comparative Measurement of the Four Lower Molars. 



Dr. Falconer's, S. erythrogenoides 



Dr. Nehring' s /S. ^/^aicMs, No. 1 



No. 2 



Brit. Mus. recent iS. ^?teicMs, No. 1 ... 



No. 2 



Dr. Nehring's S. citillus 



Brit. Mus. recent S. citillus 



Coll. Surg, recent »S. Jfo«^ofeM, No. 1 



No. 2 



Norfolk fossil form at least 



13-4 



mm, 



11-5 





11-3 





11-0 





10-2 





8-5 





8-5 





10-2 





9-2 





11-5 





