586 MR. M. F. WOODWARD ON [May 5, 
the base of this structure, the metacone and subsequently the 
hypocone being similarly derived from a backward extension of 
the base of the primitive dentinal germ. This primitive dentinal 
germ has, I believe, primarily a somewhat conical form in all cases, 
and one of the cusps of the adult tooth appears to be the direct 
continuation of this primitive cone, the remaining cusps being 
outgrowths usually from its base. It is not customary to find a 
blunt expanded table-like dentinal germ from which the cusps 
arise as secondary outgrowths—a condition which, it appears to 
me, must be necessarily assumed to support Osborn’s view that 
the protocone is primary but retarded and the paracone its lateral 
derivative accelerated. 
If it be the case that the paracone in the majority of Mammalia 
is the direct continuation of the primitive dentinal germ, and 
therefore of the single cone of the protodont mammalian ancestor, 
then we have the apparent anomaly of this primary cone giving 
rise, in the majority of forms, to the so-called paracone, 7. ¢. the 
antero-external cone, while in a few it persists as the so-called 
protocone (antero-internal cone), a condition which suggests that 
the usually accepted identification of the cones of the upper molars 
is not in all cases the correct one. 
It may be possible that in the above too much stress is laid on 
the ontogeny of the molar cusps; but, on the other hand, do we 
know sutlicient of the phylogeny, as deduced from paleontological 
evidence, to prove that the primitive cone has in all cases been 
correctly identified in the upper molars? For though we have, 
thanks to the researches of Owen (17), Osborn (16), and Marsh (11), 
knowledge of a great number of Mesozoic mammals, yet the molar 
teeth found are nearly all lower ones, and but few upper molars (save 
multituberculate ones) are known until we reach Tertiary times, 
when the teeth have assumed forms whose cusps can be more 
easily homologized with those of living mammals than with the 
cusp or cusps of the Reptilian tooth or with that of the ancestral 
mammal. So that with regard to the evolution of the upper 
‘molars we are almost completely in the dark, for we know of no 
Triassic or Jurassic protodont upper molars, but three maxille 
(I believe) containing triconodont teeth, and but a few which, 
according to Osborn, contain trituberculate teeth. 
I have tried to ascertain the exact number of upper jaws of 
Jurassic mammals possessing tritubercular molars or teeth approxi- 
mating to that type, but have been unable to disperse the mystery 
which seems to envelop them. In England we certainly possess 
one specimen, which was described by Owen (17) as Peralestes 
longirostris, and is preserved in the British Museum; with this 
Owen associated a lower jaw which is now separated by Lydekker 
(10) from this form and assigned to Amblotherium mustelula. Owen 
also described four upper jaws,which he referred to Stylodon pusillus ; 
* Several isolated upper molars are known from the Upper Cretaceous rocks 
of N. America; some of these are said to be trituberculate (Osborn, “ Mammals 
of tthe Upper Cretaceous Beds,” Bull. Amer. Mus. Nat. Hist. 1893, p. 311), 
notably Didelphops, but this, though triangular possesses at least 6 cusps. 
