DESCRIPTIONS -OR” NEW (SPECIES “OF  DIPLODUS 
TEETH. FROM THE DEVONIAN OF NORTHEAST- 
FERN ILLINOIS 
ISOLATED tricuspid teeth with a minute median denticle, sim- 
ilar to those of the Carboniferous and Permian genus Pleuracan- 
thus, are provisionally grouped under the name of Dzplodus, and 
it has been customary to distinguish the so-called Diplodont 
and Cladodont types of Elasmobranch dentition according to 
the relative sizes of the median and lateral cusps. But since the 
discovery of Chlamydoselache in recent seas and the remarkable 
Pleuropterygi from the Cleveland Shale (Upper Devonian), it 
appears that the above types of dentition were common to sev- 
eral groups of primitive sharks, thus vitiating all generalizations 
based on the distribution of detached teeth. That species 
founded on such variable and fragmentary remains can have 
only a provisional value, pending the discovery of other parts of 
the skeleton, is further emphasized in the case of some Pleuracanth 
fishes, which have several forms of ‘‘ Diplodus”’ teeth occurring 
in different parts of one and the same mouth. 
As will be pointed out in the following, there are forms of 
Phoebodus teeth intermediate between Dzplodus and Cladodus. 
This is interesting on account of the close parallelism displayed 
by teeth adapted for piercing among more or less widely sepa- 
rated groups, but as for throwing light on the interrelationships 
of these ““genera”’ is wholly without significance. ‘The earliest 
and most primitive forms of piercing teeth are typified by Profo- 
dus and Dolodus from the Lower Devonian of Campbellton, 
New Brunswick. Cladodus is first met with in the Corniferous 
limestone of Ohio, and the two new Lzplodus species described 
below are the oldest known representatives of that genus. Mr. 
Stuart Weller, who discovered the material and kindly invited 
its description, regards the horizon as Uppermost Devonian. 
The locality is near Elmhurst, Illinois. 
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