ISOTELUS, ACROLICHAS, CALYMENE, AND ENCRINURUS 69 
The specimen described first by Locke consisted of a fragment 
of the reflexed margin or doublure of the posterior part of the 
pygidium; this fragment was 5 inches long and If inches wide, 
and it was marked by veins,’’ but its curvature was so small 
that it suggested ^The end of an ellipse 22 inches long and 12 
inches broad.” The posterior termination of the axial lobe could 
be recognized. All of these features are represented in figure 
8, accompanying Locke’s original description of this species 
(see also fig. 1 on plate XVII of this publication), but other 
features are added so as to indicate the relative position of the 
fragment in the pygidium. Essentially, nothing is known about 
this type except that its posterior margin was of small curvature. 
So little of the pygidium is preserved that it is impossible to 
determine the ratio of the length of the latter to its width. As 
a type it is worthless. 
The specimen described second by Dr. Locke (fig. 9 accom- 
panying his original description; see also figure 2 on plate XVII 
herewith), consisted of an entire pygidium about 3| inches in 
length, but this pygidium was enlarged by Dr. Locke to twice 
its natural size, and a thorax and cephalon, based on Isotelus 
megalops Green (Mon. Tril. N. Amer., 1832, p. 70, cast No. 25), 
was added, producing a drawing 21 inches in length. Only the 
pygidium of this drawing belongs to Isotelus maximus, and this 
pygidium is distinctly more elongate and more triangular than 
the pygidia of the Huffman Conservancy dam and Roaring Run 
specimens described above, the ratio of length to width of Locke’s 
specimen being about 65 per cent. 
Although the more perfect pygidium, found by Dr. Locke, 
was described and figured by him second, it is the only one of 
the two specimens sufficiently complete to serve as a basis for 
the identification of other specimens, the first specimen suggest- 
ing merely large size but no other specific characters. On this 
account figure 9 of Locke (fig. 2 on plate XVII of this publica- 
tion) is chosen as representing the type of Isotelus maximus; 
figure 8 may belong to the same species as the Huffman Conser- 
vancy dam and Roaring Run specimens, described here, but 
there is no means of determining this with certainty. 
