SIWALIK AND NARBADA PROBOSCIDIA. 
45—226 
on the worn crown surface presenting irregularly, or somewhat triangular, in place 
of trefoil-shaped islets, as well as by the presence of large quantities of cement in 
the valleys. The second and third lower true molars of Mastodon angustidens ^ are 
much simpler teeth than the corresponding teeth of M. pandionis (Plates XXXIV, 
XXXV, fig. 4). In the latter the valleys are completely blocked by outlying 
tubercles whereas in the former they are tolerably open. There is a very small hind- 
talon in the penultimate molar of M. angustidens, and a very large one in that of 
M. pandlonis : in the last molar of the latter species the hind talon is developed into 
a fifth ridge, whereas in M. angustidens there are generally only four ridges in the 
last molar, with a very small hind-talon : M. pandionis in these respects is evidently 
transitional between the Trilophodons and Tetralophodons. A penultimate lower 
true molar of M. angustidens figured by von Meyer ^ has a larger hind-talon than 
in the last mentioned specimen ; this talon, however, is in the form of an elongated 
cingulum, and quite different from the two-coned talon of M. pandionis ; the whole 
tooth of M. angustidens is of less complex structure than that of M. pandionis. That 
the two species are closely allied is, however, evident from the general structure 
of the molars and the mandible. 
M- productus. — The mandible of the trilophodont M. productus of the Loup- 
fork group of New Mexico^ has a produced tusked symphysis which has more 
resemblance to the tusked symphysis drawn in fig. 2, of Plate XXXVI of this 
memoir, and provisionally referred to M. pandionis. In M. productus (Plate LXX 
of Cope’s memoir) the tusks are straight, and have their largest diameter in the 
transverse, and not in the vertical direction, in which respect they differ from the 
tusked mandible referred to M. pandionis. The molars of M. productus are smaller 
and of simpler structure than those of M. pandionis, and the last molar has only 
four ridges, without a hind-talon. 
Mastodon pandionis does not approximate closely to any other described species 
of Trilophodon in its dental and mandibular characters. 
Mastodon siralensis . — Curiously enough the last lower molar of this species 
has a most remarkable resemblance to the corresponding tooth of the tetralopho- 
dont Mastodon sivalensis, as may he seen by comparing this tooth of M. pandionis, 
represented in fig. 4 of Plate XXXV, with the corresponding tooth of the same 
side of the jaw of M. sivalensis represented in fig. 3 of Plate XLIV. Both teeth 
appear to have the same number of ridges, though in the former the last ridge 
(from the characters afforded by the penultimate molar) is described as a talon, and 
in the latter (from the same considerations) as a true ridge. Both teeth agree 
in the general form of the ridges, of the columns, and of the accessory columns, 
and also in the general shape of the dentine islets : the main difference between 
the two teeth being that the molar of M. sivalensis is somewhat narrower than 
’ “ Abhandl. der. k. k., Geol. Reick.” Wien 1877, Vol. VII, Pt. 4, Plate IV, fig. 2. 
- “ Palseontographica”, Vol. XVII, pi. IV, fig. 6, 
*Cope: “Extinct Yertebrata of New Mexico,” United States Geographical Survey, west of 100th meridian, 
Vol. IV, pt. II, p. 306, Pis. LXX— LXXII. 
M 
