150 Frederick Chapman: 



Pulp cavity moderately deep. Root entirely covered with cement. 

 Crown bevelled on inner, concave side and surface radiately 

 grooved. 



Scapfodon lorlderi, gen. et. sp. nov. (Plate XXVII., Figs. 1-3). 



Description. — Tooth (mandibular), large, conical, tapering from 

 a wide base to a narrow crown; much depressed and widely curved, 

 in basal section, long elliptical. The base is open, and has a mode- 

 rately deep pulp cavity. The whole of the root, so far as pre- 

 served, was covered with a fairly thick layer of cement ; the sur- 

 face is relieved by a series of shallow longitudinal furrows extend- 

 ing from the base through more than half the length. The crown 

 can scarcely be separated, being continuous in contour, with the 

 root, and is apparently marked off at the limit of the tevel. The 

 apex of the crown is bevelled to a sharp cutting edge towards the 

 convex side, the bevelled surface being marked with some low 

 radiating ridges producing a few serrations on the cutting edge,, 

 the latter having a parabolic curvature. 



Measurement. — Length of tooth, measured along the convex face,. 

 113 mm. Greatest width of tooth at base of root, 41 mm.; width 

 at base of bevel, 13 mm.; thickness at base of tooth, 19.25 mm.; 

 thickness at base of bevel, 7.5 mm. ; depth of pulp cavity, 36.5 

 mm. ; weight, 46.5 dwts (troy), or 161 kilogrammes. 



Microscopic Structure of the Tooth. — A thin transverse section 

 was taken through the wall of the tooth at the base, bordering the 

 pulp cavity. The intermediate layer is of the nature of ivory like 

 that of the Cachalot,^ and the outer and inner margins, each about 

 one quarter of the thickness of the middle layer, show the structure 

 of cement. Under a 1-inch objective (about 52 diameters), the 

 cement layer, about 5 mm. in thickness, is homogeneous in struc- 

 ture, but in this specimen is crowded wlith ramulose borings of a 

 parasitic fungus, the hyphal tubes being filled with dark material, 

 probably due to the grinding; isolated spores are also seen here 

 and there. 



The intermediate layer, the dentine or ivory, shows a dense 

 structure composed of a closely set series of minute dentinal tubes 

 transversely arranged, whilst circumferentially, or crossing these 

 tubes, are parallel lines of greater density at varying distances, 

 probably contour lines. The intermediate ivory layer in the slide 

 examined measures 2 mm. in width. 



1. See Owen. Odontography, 1845, p. S.'ifi, pi. Ixxxix., fij.'. '2. 



