126 
THE GEOLOGIST. 
identifying the lower jaws with the forms to which they belong. IN"© 
specific dissimilarity in size or position of the teeth meeting each 
other has been noticed by me. None of the limb-bones can be iden- 
tified to belong to the same individuals as the crania or lower jaws. 
I give the characters of the genus from Gervais, and the synonyms 
according to my own views : — 
CaixotheeiIjM, Bravard. 
7 
" Teeth in continuous series ; certainly — molars [= premolars 
4 4 3 3 _ * 
molars 333]? four toes, of which the two median digits are t1ie 
largest, and similar to each other; the two last very slender." — Ger- 
vais, loc. cit. 
1. Caii^otheeium coMMrxE, Brav. memoir on Cainotlierium = 
following species : — C. laticurvatum^ Pomel, loc. cit. C. elegans, 
Pomel, I. c. C. gracile, Pomel, I. c. C. leptorhynchum, Pomel, 
' Bulletin de la Societe Geologique de Prance,' 1846, t. iii. p. 369. 
C. medium, Brav., I. c. C. oninimum, Brav., I. c, * ? Hycegulus col- 
lotarsus, Pomel, I.e. * ^ Hijceguliis murinus, Pomel, Z, c. = C. Coiir- 
toisii, Gervais. Oplotlierium laticurvatum, Laizet and De Parieu. 
Oplotherium leptognatlmm, Laizet and De Parieu. Microtlierium 
Henggeri, H. v. Meyer. Microtherium concinnum, H. v. Meyer. 
Cainotlierium majus, Pomel, MS. ? GainotTierium leptlielicium, 
Bravard, MS. ? 
2. CAiiroTHEETUM METOPiUM, Pomel, I. c. A very doubtful species. 
In British Museum ? 
The problem of specific creation and extinction can be best worked 
out upon such genera as Cainotlierium. Speculation might lead a 
Natural-Selectionist to imagine how the four-toed Cainotlieria of the 
Miocene, b}^ reason of tlieir firmer footing in a mudd}'^ soil, might have 
been able to go deeper in a river in quest of food, and have supplanted 
and caused the extinction of the JDicliohunes of the Eocene, who had 
only one small digit at the back of their foot, making three toes in all. 
The differences between, e.g. Cainotlierium., Dicliohune. Xipliodon, and 
Dicliodon, and Ap)lielotlierium, are such as we might suppose might be 
altered through the lapse of long generations. Whether such altera- 
tion was slow and gradual by Natural Selection or any similar process, 
or whether it was not rather due to a more rapid and sudden method 
of operation, is the problem which the latter half of the nineteenth 
century may perhaps solve by experiment, observation, or logical de- 
monstration. In the meanwhile, to those who bear in mind the Lin- 
nrean maxim, Omnis vera cognitio cognitione specijica innitattir,^ the 
study of the minute differences of the Cainotlieria affords an instruc- 
tive topic. 
* I have not seen any authentic specimens of these species. The C. Courtoisii of 
Gervais appears not to be specifically distinct from some specimer.s of C. commune 
t Linne, ' Species Plantarum,' 8vo, A^iudobonte, 1764, p. 3. 
