416 A Geolof/ical Section at Todd's Fork, 0. — Foerste. 
Guelph, so as to lose their distinctive character. In Indiana 
their place is taken by the Wakiron series of rocks. At Todd's 
fork nothing seems to intervene between the Niagara shales and 
the Guelph rocks, and although no single exposure is continu- 
ous enough to give the total hight of the shales themselves, it 
is very likely not more than 30 feet. 
The Guelph exposures near Wilmington are lithologically 
and paleontologically equivalent to the Cedarville beds of Ohio 
and the Niagara dolomyte of Chicago and Racine. Fossils are 
abundant, especially cephalopods. Pterinea hrisa, in its typical 
form, is also present. The genus lUanms has also several rep- 
resentatives. 
Rg5 
^^^^^^^s^^s,^fl 
Annelid Teeth. 
The annelid teeth of the Medina at Todd's fork are, as usual, small, black, 
shining bodies, often too minute to be readily discerned by the unassisted 
eye, freqently standing out in relief, entirely uninjured, upon the weath- 
ered slabs of the sandy shales. Associated with them are little sheets of a 
similar black substance, sometimes forming narrow bands, 75 mm. in width, 
and 1 1 mm. long. Such bodies are generally associated by collectors with 
graptolites, but most probably they represent the chitinous skin of the 
annelid, of which the teeth are the more tangible evidence. The teeth of 
living annelids are known to be exceedingly variable in form, according to 
their position in the mouth. Dr. Gforge J. Hinde, the first serious student 
of these forms in a fossil state, has proposed a classification into genera 
v?hich combine features similar to those of genera now living, the generic 
name of the fossil forms usually recallicg the name of some similar living 
genus. In consequence, very different forms of teeth are associated gener- 
ically. We doubt, however, whether this classification has either great 
theoretical or practical value. Combinations of teeth seen in living genera 
can scarcely with safety be presumed to have existed in types so eaily in 
