226 
ON THP] STRUCTURE AND CLASSIFICATION 
son of these teeth with the corresponding mandibles, gives us an outline of the 
correlation which is the basis of classification. 
Vtk & ^ ^ Hi & 
A a 16 7 // /i /i 
FKiURE 11. The premolar tooth forms of the mammals of the Second Group. The premolar repre- 
eented is invariably the most posterior of the series ; the anterior face is to the left. The reference numbers 
are the same as those given above for the molars, and correspond to those upon Plates VIII and IX. Nos. A, 
4 , 0, 11, 12 are seen upon the inner surface, the remainder upon the outer surface. Original. 
Incitort. 
Caninet- 
Premolars. Molars. 
Mandible. 
Tb/pical genus 
1. Erect. 
Large and erect. 
With distinct ba- W ith three stout 
sal cusps. cusps and cingu- 
lum. 
Stout, with a 
broad coronoid 
and low condyle. 
Triconodon. 
(4) 
2. Erect. 
Large and erect. 
With distinct ba- With opposed 
sal cusps. cusps. Uncon- 
nected. 
Stout. 
Peralestes. 
(Peraspcdax.) 
(9) 
3. Unknown. 
Large.* 
Small, or transi- With no cusps, 
tional to molars. Columnar. No 
cingulum. 
Unknown. 
Kurtodon. 
(16) 
4. Prorumbent. 
Small and semi- 
procumbent. 
With a “heel” With three slen- 
or cingulum der cusi>s. No 
cusps. cingulum. 
Slender, with a 
narrow coronoid 
and high con- 
dyle. 
Ambloiherium. 
(11) 
5. rrocnnibcnt. 
Small and semi- 
procumbent. 
AVith a “heel” With opposed 
cusps. Con- 
nected. 
Slender, with a 
narrow coronoid 
and high con- 
dyle. 
Stylacodon. 
(12) 
Tliese genera are typical not only of families but in a less degree of Sub-Groups. 
As remarked before, the same degree of functional specialization for insectivorous, 
carnivorous or otlier diet is not by any means observed in all the allied genera, yet 
we maj broadly attribute this specialization to the entire sub-group as a general 
characteristic. The sub-groups were the Insectivora, Carnivora, etc., of the mesozoic 
l>eriod ; not in the recent sense of these terms, but in relation to their feeding habits. 
SUB-ORDER PRODIDELPHIA.— Haeckel.2 
Primitive Marsupials, generally distinguished from the recent forms by the 
fn.<jucnt ,,ro«„ce of four premolars arrd numerous molars. Molars with distinct 
multiple fangs ; molar crowns not fiUly tritubercular or tubercular-arctorial. 
( .tRNiyonous and Omnivorous SuB.GRonp._The mammals which are included 
m tta sulugroup have many points of mutual resemblance, although upon the first 
exam matmn they appear to differ widely. They sub-divide into two series 
era ail J,le r'^’ ^ includes all the largest gen- 
em and some of inter mediate sire, and is d istinguished by the primitively sectorial 
* Thw tooth 18 imssibly an incisor. 
pof- ithout definition in the History of Creation,” and provisionally defined and adopted here. 
