NOVEMBER 10, 1898. ] 
probably not yet received their share of the 
attention of collectors. Of rodents there 
are now living in North America over 300 
species, of bats about 40 species, and of in- 
sectivores about 40 species. 
Devonic. 
‘Ordovicic. Siluric. 
SCIENCE. 
Subearbonie. 
683 
tions of the Devonic and Carbonic would 
not have been greatly increased. The oc- 
currence of so many defensive spines in the 
Subearbonic, when such a variety of elas- 
mobranchs is indicated by teeth, is a pretty 
Mesozoic. 
Carbonic. Tertiary. 
Diagram showing the distribution of North American fossil fishes. 
The animals which are included under 
the general name of fishes furnish such in- 
teresting results that an attempt is made to 
furnish a graphic illustration of the time 
distribution of the principal groups. In ex- 
amining this we are at once struck with the 
enormous development of the elasmobranchs 
during the Subcarbonic period. Further- 
more, from the elasmobranchs presented in 
the illustration have been excluded the 
ichthyodorulites, the great majority of 
which are undoubtedly the defensive spines 
of shark-like animals. The distribution of 
the species of these is as follows: Siluric, 2 ; 
Devonic, 27; Subcarbonic, 83; Carbonic, 
including the Permic, 22. Had these been 
included, the Subcarboniec peak would have 
been uplifted by an amount equal to two- 
thirds its present height, while the eleva- 
plain suggestion that in very many cases a 
genus founded on a spine is identical with 
some other genus based on teeth; for it is 
not probable that many of the ichthyodoru- 
lite-bearing fishes were toothless. After the 
Subcarbonic period the elasmobranch line 
descends rapidly in the Carbonic, slowly in 
the Mesozoic, and rises slightly in the Ter- 
tiary. At the present day there are recog- 
nized only about 86 species of elasmobranchs 
living along the whole American coast, 
north of Mexico. 
Although the ichthyodorulites have been 
excluded from the elasmobranch species in 
the illustration, the line has been extended 
to the Siluric, because of the occurrence of 
Onchus in it. 
In like manner the line representing the 
Placodermi and the Crossopterygia have 
