70 The American Geologist. August. 1*93 
pieces niid all the smaller pieces beyond number 17 are want- 
ing. Of these smaller terminal pieces there were almost cer- 
tainly as many as eight, making twenty-five in all. 
Of the hind feel neither of the cuboids and none <>!' the cu- 
neiforms <>r other smaller tarsals were found, hut from the 
articular surfaces of the calcaneum, tile astragalus and the 
proximal ends of the metatarsals, their size and nature are 
reliably determined. The other absent portions of the hind 
feet are indicated by the omissions in the parts already named. 
Enough are in hand to show all the. characters of these skele- 
ton feet except that none of the distal phalanges were found. 
There is sufficient hasis however for a very reliable inference 
as to their form and size. 
There are indications that the larger and medium sized 
tail vertebrae bore on their under sides the chevron bones 
characteristic of a number of species of vertebrates, but of 
these none were preserved. 
T'. Some Special Points of Structure. 
The double posterior nares may well he noted by all who 
write the cranial anatomy of Castoroides, since, in all the do- 
main of the mammalia through their whole range in time we 
find no other species presenting the same structural feature. 
Look at the basal region of a skull of the ground hog (Arcto- 
mys monax) and you will note that the internal pterygoid 
blades o/>/>i-<nir/, each other slightly near their middle. Imag- 
ine them to be plastic so that you can press them together in 
the middle making them weld hut leaving them separate fore 
and aft. and you will have essentially the double posterior 
nares of Castoroides; the one antero-inferior, the other 
postero-superior. 
The compound character of the molars, though by no means 
peculiar to tin- species, may still he worthy of note here. 
These teeth are severally made up of three to four flattened 
cylinders of enamel enclosing dentine and surrounded by ce- 
ment by which they are held together. They are quite simi- 
lar in this respect to the grinders of the Mammoth except 
that in the latter the numerous plates, in addition to being 
cemented together are united to a common basement near the 
fangs. 
