874 The American Naturalist. [October, 
No interclavicle ; coracoid very small, coossified 
with scapula; not reaching sternum ; Eutheria. 
Of the Prototheria, there are probably three orders of which 
species are known, but the location of the two first enumerated 
below is not certain. 
Incisors reduced ; molars with compressed cutting 
crowns, and undivided roots ; Protodonta. 
Incisors enlarged ; molars with tubercular grind- 
ing surfaces, and distinct roots ; Miiltituberculata. 
No true teeth at maturity ; Ornithostomi. 
The families are the following : 
Protodonta ; Dromatheriidae. 
Multituberculata ; Tritylodontidae, Plagiaulacidae, Chirogidae, 
Polymastodontidse. 
Ornithostomi ; Ornithorhynchidae, Echidnidse. 
The Eutheria are represented by the following numerous 
I. Marsupial pelvic bones (generally); palate perforated; 
(vagina double ; placenta wanting ; corpus callosum 
rudimental ; cerebral hemispheres small.) {Didelphia) 
One deciduous molar tooth ; Marsupialia. 
II. No marsupial bones ; palate generally entire ; (one vagina ; 
placenta and corpus callosum well developed.) {Mono- 
delphia.) 
A. Posterior limbs wanting, or represented by minute , 
rudiments ; anterior limbs oar-like. {Mutilata) 
Elbow joint inflexible ; carpals discoid, and, with 
the phalanges, separated by cartilage ; lower 
jaw without ascending ramus ; Cetacea. 
Elbow joint flexible ; carpals and phalanges with 
close articulations; mandible with ascending 
AA. Posterior limbs present ; ungual phalanges 
compressed and curved on one or all the feet' 
( Unguiculata) 
» Except Mesonychidae. some Glires, and posterior feet of some Edentata. 
