446 Recent Literature. [July, 
think is quite indefensible. In this chapter Prof. Gaudry dis- 
cusses the flints found -by the Abbé Bourgeois in the Middle 
Miocene (Calcaires de Beauce) of Loir-et-Cher, concerning which 
opinions so differ. They are regarded as works of art by many 
archeologists, among whom are cited MM. de Vibraye, de Mor- 
horizon not much above the Oregon beds of our White river 
formation. As Gaudry remarks, no species of Mammal of that 
period still exists; and he adds, “ it is not probable that the cut- 
ters of those flints remained the same amid universal change.” 
His concluding words are as follows: “If then it is to be shown 
that the flints of the Calcaire de Beauce, collected by the Abbe 
Bourgeois have been cut, the idea which presents itself most 
naturally to my mind is, that they were fashioned by the Dryo- 
pithecus.” 
As a popular and at the same time scientific exposition of the 
succession of Mammalian forms, as displayed by their structural 
details, this book has no rival. The author has been led, like 
most other thorough students, to adopt the doctrine of evolution, 
and some of his reasons are here clearly set forth. The work is 
distinguished for the excellence of its engravings and typography. 
RYDER ON THE MecHanicaL Genesis oF Toora Forms.’—In 
the several articles relating to this subject Mr. Ryder has made a 
valuable contribution to the doctrine of evolution. He adopts the 
classification of teeth proposed by Cope, and endeavors to explain 
by mechanical laws the succession or phylogeny of the various 
existing dental types pointed out by the same author. The appli- 
cation of mechanical theory to this question is ingenious, and 
results in some very probable hypotheses. First among these 1S 
the supposed effect of lateral pressure in flattening conical cones 
or cusps so that their section becomes semicircular or crescentic. 
Another is the probable crowding of tubercles on each other by 
impact transverse to their direction, producing plicate structure. 
- His conclusions may be stated more in detail, and are as follows: 
t in Carnivora and Omnivora the jaws were simply 
tubercles or cusps composing the teeth do not to any extent og 
depart from the short-rooted type with conical tubercles, styled 
by odontologists bunodont. That the distance apart of the series : 4 
of molars of opposite sides, of both upper and lower series, WaS — 
1On the Mechanical Genesis of Tooth Forms. By Jonn A. Ryper. Proceedings 
of the Academy Natural Sciences, Philadelphia, 1878, p. 45. Further notes on do. 
Loc. cit., 1879, p: 47. 4 ae 
