132 Reviews— Prof. Osborn—On Mesozoic Mammals. 
SEVREG VL Ea Vis. 
—_@—__—. 
T.—On tHE STRUCTURE AND CLASSIFICATION oF THE Mrsozor1o 
Mammatta. By Dr. Henry F. Osporn. Proc. Acad. Nat. Sci. 
Philadelphia, June 21st, 1887. 
HIS paper is an outline of Professor Osborn’s observations 
“upon the structure of the British Mesozoic Mammals and a 
Classification of the Mesozoic Mammals in general, in view of their 
relationship to each other and to recent orders.” The author, who 
is well known by his numerous paleontological and morphological 
researches conducted in the Princeton College laboratories, has had 
the opportunity of examining the type-specimens of all the Mesozoic 
Mammals hitherto described, except four. The results of so 
extended a study are thus of unusual interest and significance. After 
some preliminary remarks, a series of notes are offered upon the 
English fossils, described by Owen; and the succeeding larger 
section of the paper is occupied with a general scheme of classification. 
Referring first to the Stonesfield Slate jaws, Dr. Osborn remarks 
that three distinct genera are commonly included under the name 
Amphitherium. The molar of Amphitherium proper (type A. Prevostit) 
is bicuspidate, with a low posterior heel; that of Amphitylus, gen. 
nov., has three blunt cusps and an internal cingulum ; while that of 
Amphilestes, Owen (type A. Broderipii), has three prominent cusps, 
and a pronounced cingulum, encircling the crown. The lower dental 
formula of Phascolotherium is given as 1. 4, c. 1, pm. 0, m. 7. 
Triconodon is the first Purbeck genus remarked upon. Dr. Osborn 
points out that in this primitive form, the fourth premolar early 
replaces a molariform milk-tooth, and the fourth true molar is very 
late in rising, thus agreeing precisely with the mode of succession 
determined by Professor Flower in certain existing Marsupials. 
Triacanthodon consequently becomes a synonym of Triconodon. 
Phascolestes is considered to be quite distinct from Peralestes, and 
Leptocladus from Stylodon. Spalacotherium has the lower dental 
formula, i.? 2, c. 1, pm. 4,m.6. The maxilla referred by Owen 
to Stylodon must be removed to a distinct genus, Kurtodon,' charac- 
terized by the compact arrangement and peculiar wearing pattern of 
the crowns, and a new enlarged figure is given in illustration. The 
maxillary formula of Bolodon is found to be i. ? 2, c. 0, pm. 3, m. 4, 
and the characters of these teeth are also shown in a woodcut. 
The following is a synopsis of the proposed classification :— 
I. Mutrirupercutata.—One incisor greatly developed at the 
expense of the others and of the canine; diastema, varying in width, 
in front of the premolars; molars characterized by two or more 
antero-posterior rows of tubercles separated by longitudinal valleys 
or grooves. 
Fam. 1. Plagiaulacide. Ctenacodon, Plagiaulax, Ptilodus. (Also the Tertiary 
Neoplagiaulax.) 
Fam. 2. Bolodontidse. Bolodon, Allodon. 
Fam. 8. Tritylodontide. Tritylodon. 
1 Tn the original paper, the preoccupied term Athrodon is employed. This is 
replaced by Kurtodon in the ‘‘ Amer. Nat.,’’ Nov. 1887, p. 1020. 
