ON JANASSA BITUMINOSA. 853 



tliose of the upper jaw. At the posterior part of the general 

 mass several of the second primary and petalodontoid teeth lie 

 scattered about, chiefly with the under surfaces uppermost. 



The remaining specimen (PI. X., fig. 1) to be noticed, though 

 consisting only of a few teeth, is very interesting, inasmuch as 

 it displays in profile an entire vertical row lying in almost exact 

 order, one resting upon the other. The whole length of the 

 teeth is seen, fi'om the cutting-margin to and including the root, 

 bent in a deep sigmoidal curve. The series appears to be of 

 the central teeth : four lie in close contact, the back or under 

 surface of one individual resting upon and fitting exactly to the 

 face or upper surface of that immediately below it. A very im- 

 jjerfect fragment of a fifth tooth is seen pressed to the under 

 surface of the fourth of the series ; and in front considerable 

 portions of two lateral primaries lie with their under surfaces 

 uppermost, one of which exhibits in a remarkable manner the 

 transverse grooves caused by the rubbing of the crushing-disk 

 of the tooth on that supporting it. Similar transverse grooves 

 can be seen on one or two other teeth of the series. A consi- 

 derable fragment of a second primary lies near the centre of the 

 row. 



The minute structure of the teeth is rather peculiar ; and 

 though we have not examined it in the entire tooth, and though 

 our account of it must necessarily be imperfect, as it is from 

 mere fragments, yet we cannot refrain from saying something 

 on the subject. 



We have stated that the upper surface (namely, the anterior 

 scoop-like margin and the crushing-disk) is covered with a layer 

 of opaque-white enamel-like matter. This coating is thickest 

 over the crushing- disk, where it is of a considerable depth. 

 When the tooth is quite fresh, there appears to overhe this a 

 thin film of transparent enamel. The interior is composed of a 

 rich brown-coloured substance, which may be looked upon as a 

 form of dentine, made up of large, branched and anastomosing 

 tubes with thick walls, which, for the most part, run lengthwise : 

 their cavities are undoubtedly medullary channels ; they are nar- 

 row in proportion to the thickness of the entire tube. These 



