778 
lar shape with occasionally angular points. The radiating fibres were 
numerous, ranging in all directions ; and the independent transverse 
fibres were also numerous, traversing witha curved course the whole 
substance. ‘The cells of the interspaces were visible. The enamel 
on the upper tusk was a line thick. The parallel rows of constituent 
cells throughout the external half ranged in straight lines, but 
throughout the internal half they were curved diagonally. There 
was no clear space between the enamel and ivory, but the line of 
junction was well defined. A plumose layer of fibres, apparently the 
peripheral termination of the main undivided fibres of the ivory, suc- 
ceeded to the enamel. The component bulbs of the fibre were round, 
but not often visible, and were best seen in the longitudinal section. 
The fibres were placed at about the distance of two interfibral spaces, 
and curved in the transverse section as well as in the vertical, but in 
the latter direction slightly. A minute corpuscular appearance was 
scattered over the substance, and the cells of the interfibral material 
were visible. 
The crusta petrosa, enamel and ivory of the under tusk were similar 
to those of the upper, except that the constituents were so transpa- 
rent as hardly to betray any characteristic. The parietes of the cells 
of the enamel are more defined in the under tusk. 
Besides the important characteristic of the thick coating of enamel, 
the tusk of the T.Godmani presents manifest differences from that of 
the other species, in the elements of each of the constituents. ‘The 
radiating fibres of the corpuscules differ from those of Mastodon gi- 
ganteum in being given off equally in all directions; in the M. gigan- 
teum the numerous independent fibres of the T. Godmani are also 
absent, and the zones or belts of minute corpuscules in the ivory of the 
M. giganteum are wanting in that of the 7. Godmani. 
Tetracaulodon Kochii.—The tusks of this Pachyderm have only two 
constituents, crusta peirosa and ivory. The crusta petrosa varies in 
thickness, equalling in some parts an inch. In the vertical section 
the corpuscules are irregularly oval and irregularly disposed at the di- 
stance of three or four corpuscular diameters, and they give off occa- 
sionally many fine radiating fibres. Numerous independent trans- 
verse fibres pass in a curved direction also throughout the substance, 
their beaded or minute corpuscular appearance being very visible, 
and they are of an irregularly twisted oval form. The cells of the 
interspaces are likewise visible. 
The ivory of the upper tusks consists of very slightly undulating, 
undivided fibres, with the cells of the interfibrous substance well 
marked, but semi-transparent. The fibres of the under tusk slightly 
undulate, and present occasionally an appearance of thorny projec- 
tions. The compartments of the fibres are easily seen, and are irre- 
gular in size, but rounded. 
Tetracaulodon Tapiroides.—The tusks consist also of only crusta 
petrosa and ivory, and the resemblance in the microscopic structure 
of this species with that of T. Kochii is great. The thickness of the 
crusta petrosa is considerable. The very irregularly-shaped corpus- 
cules, placed at intervals of two or three corpuscular diameters, are 
