70 
AUG. F. FOERSTE 
Apparently there are two species of Isotelus present in the 
Liberty and Waynesville members of the Richmond of Ohio 
and adjacent states. One of these has more elongate cephalons 
and pygidia, and is represented by the pygidium used by Dr. 
Locke for his figure 9. For this species the name Isotelus max- 
imus is retained. The second species, represented by the Huff- 
man Conservancy dam and Roaring Run specimens, has rela- 
tively shorter cephalons and pygidia and is regarded as a distinct 
species for which the name Isotelus hrachycephalus is proposed. 
A large pygidium of Isotelus resembling in outline that of Isotelus 
maximus (fig. 9 of Locke), was found in the Stony Hollow, 
northwest of Clarksville, Ohio, by Prof. S. R. Williams of Miami 
University. Imbedded in the same slab is Hehertella insculpta, 
and it was found at the extreme top of the Waynesville member 
of the Richmond group. This pygidium is 5| inches long and 
7 inches wide, thus indicating that Isotelus maximus actually 
attains as large a size as Isotelus hrachycephalus, and is not con- 
fined to the smallbr size usud by Locke for his figure 9. 
It is customary to refer Isotelus megistos Locke (Amer. Jour. 
Sci., 42, 1842, p. 366, pi. 3; see also plate XVI of this publica- 
tion) to Isotelus maximus Locke. This is natural since Locke 
himself included the two type specimens of Isotelus maximus 
in his description of Isotelus megistos. However, the original 
description of Isotelus megistos begins with a description of a 
specimen found by Wm. Burnett on the hills at Cincinnati, and 
this is the specimen figured on the plate accompanying Locke’s 
paper. The horizon at Cincinnati apparently was not in the, 
Richmond but in the upper half of the Maysville formation, 
possibly in the Corryville. Compared with Isotelus hrachy- 
cephalus both the cephalon and the pygidia of Isotelus megistos 
are more elongate. The eyes are located nearer the posterior 
margin of the cephalon, and the anterior parts of the facial 
sutures are much more distant from the anterior margin of the 
cephalon. The space between the facial sutures, anterior to the 
eyes, is much more elongate. From this it seems evident that 
the specimen described by Locke from the Cincinnati hills 
belongs to a distinct species, for which the name Isotelus megistos 
might be retained. 
