1892.] Geology and Paleontology. 759 
and species of Multituberculata, Meniscoéssus conquistus. Since then 
, Prof. Marsh has described several species from the same formation, 
exaggerating the number very considerably, as has been precisely 
shown by Prof. Osborn. I now introduce to notice another species, 
which represents a new and peculiar family of Marsupialia or Mono- 
tremata, and which throws considerable new light on some of the 
species described by Prof. Marsh. The material in my possession con- 
sists of a mandibular ramus of the left side which is nearly complete, 
and which contains three premolars with alveoli of the anterior pre- 
molar and canine, and a fragment of the last true molar; with another 
true molar. About one hundred feet from this specimen was found a part 
of the right maxillary bone containing an entire last premolar with 
parts of the penultimate premolar, and first true molar; a molar 
lacking the protocone was found close to thjs fragment, and evidently 
belongs to it. So close is the resemblance in character between the 
teeth of the two jaws, that I am satisfied that they belong to the same 
species, and probably to the same individual. 
THLAODON PADANIcUS.—Gen. et. sp. nov. Char. Gen.—Dental 
formula, I. $; Ci; P.m. +; M. 2. Inferior canine robust, one 
rooted. Premolars rzsz two-rooted; ‘~ three-rooted. Posterior pre- 
molar each jaw with robust, convex, swollen crowns, without 
heels or accessory cusps. Superior true molar tritubercular, 
with large internal cusps, and small external cusps; inter- 
mediate cusps present. Inferior premolars 2-4 with transverse 
crowns. Inferior true molar with anterior trigon and posterior 
basin ; the former transverse, the latter with posterior angular cusps. 
The genus Thleodon represents apparently a new type of Marsu- 
pialia, or possibly of Monotremata. In the entire absence of the 
mandibular angle it resembles Ornithorhynchus, and also the genus 
Triconodon Owen, and several other genera of the Jurassic system. It 
differs from most of the genera of the Jurassic non-Multituberculata, in 
the normal number of its teeth; which apparently agrees with that 
typical of the class; viz. I. 3; C. 1; Pm. 4; M. 3. The namber of 
true molars may be four, but the space which is preserved in the lower 
jaw is as appropriate to three; either number requiring that the teeth 
should present somewhat unequal dimensions. The form in any case 
indicates an ancient and inferior type, specialized in the direction of 
dental reduction, and in the development of a molar or crushing type of 
premolars. The true molars are also specialized in the direction of 
modern forms, the superior being tritubercular, and the inferior 
