PLATE XVII 
Fig. 1. Isotelus maximus Locke; one of the types figured by him in Geol. Surv. 
Ohio, 1838, pp. 247-249, plates 8 and 9. As the first published figure, this should 
be the type, but of this entire figure only that part was based on an actual speci- 
men which is included in the marginal part of the pygidium, where the lower, 
reflexed doublure is shown by the removal of the upper part of the pygidium. 
This part is not regarded as sufficient to determine the outline of the pygidium. 
All of the remainder of the drawing was added to ‘^place’The fragment in its 
proper surroundings in the pygidium. Found in the Liberty member of the 
Richmond, on Treber Run, 8 miles southwest of Peebles, Ohio. 
Fig. 2. Isotelus maximus Locke; the second one of the types figured by Locke, 
as figure 9, found at the same locality and horizon as the preceding specimen. 
Copied from the enormous figure, 21 inches long, presented by Locke. This 
figure was based on a single pygidium, much smaller than the figure, the outline 
being based on the entire pygidium at hand and the size being enlarged so as to 
conform with the imagined size of the individual of which figure 8 illustrates only 
a fragment. Probably two species are represented by figures 8 and 9 of Locke. 
Of these, figure 9 is the only one including enough of an individual to make pos- 
sible the identification of the type. In the opinion of the writer, either Locke’s 
name, maximus, should be dropped or the name should be attached to the speci- 
men represented by figure 9, which there is some chance of identifying, in the 
entire absence of Locke’s types. 
Fig. 3. Acrolichas (?) shideleri sp. nov. A, upper surface of a fragment re- 
garded as a free cheek. B, under surface of a second, similar free cheek. Found 
in the Whitewater member of the Richmond, at McDill’s Mill, 9 miles north of 
Oxford, by Prof. W. H. Shideler. 
Fig. 4. Acrolichas cucullus ottawaensis var. nov. A, cranidium; B, pygidium. 
From the Trenton at Hull, opposite Ottawa, Canada. Collected by J. E. Narra- 
way. Differing from the type chiefly in the rounded free tips of the ribs on the 
pygidium. 
