CORRESPONDENCE. 399 



2. A well-preserved left lower molar from a peat bed in Jack- 

 son county, Michigan. 



This tooth presents a marked longitudinal convexity on the 

 outer side, while the inner side, in the vicinity of the crown, is 

 nearly straight to the posterior third, when it becomes somewhat 

 concave internally. The grinding surface is deeply concave — the 

 middle being depressed nearly an inch below the extremities, and 

 about one third of an inch below the adjacent sides. The grinding 

 surface, moreover, is twisted so that its plane, near the posterior 

 extremity, makes an angle of about 15° with the same plane near 

 the anterior extremity, the crown being more turned outwards 

 posteriorly. The five posterior plates still present traces of the 

 digitations ; in the third from the extremity are five equidistant 

 circular digitations. The posterior plate, as it penetrates the body 

 of the tooth, curves backwards and then forwards, presenting a 

 posterior convexity. The hinder plates are placed at right angles 

 with the crown-axis, but in proceeding forwards the outer ends 

 are most rapidly advanced, so that near the middle of the crown 

 the plates make an angle of only about 80° with the crown-axis, 

 and the 10th plate is duplicated in its outer half to fill up the en- 

 larged space in the outer curvature. When the tooth rests on its 

 crown and is viewed from the side, the profile is nearly an equila- 

 teral right-angled triangle, truncated two fifths of the way down 

 from the apex. The hypothenuse, or anterior slope of the alveolar 

 portion of the tooth is furnished with six short fangs produced by 

 deep folds of the dentine. The truncated portion, viewed from 

 the side opposite the crown appears to be an irregularly long cup 

 or crater of dentine, covered externally by cement, and filled with 

 the same substance to within two-thirds of an inch of the rim. The 

 cement of this tooth is nearly black, and is about .075 of an inch 

 thick on the exterior ; the dentine is light-coloured immediately 

 beneath, and quite white in its deeper substance. The enamel, 

 which projects in the plates, above both the cement and the den- 

 tine, retains a fine chalcedonic colour and lustre. 



3. Cast of a left lower molar, found near Toronto, C. W ; , and 

 obtained from Thomas Barret, of Niagara Falls, C. W. 



This tooth is curved on both sides, with the convexity turned 

 outwards. The grinding surface is strongly concave both lono-i- 

 tudinally and transversely. One strong fang on the anterior por- 

 tion of the tooth seems to have been removed. Posteriorly the ap- 

 parent removal of the deeper alveolar portion has exposed ten of the 

 plates. 



