68 
AUG. F. FOERSTE 
reached beyond the posterior margin of the third thoracic seg- 
ment, possibly as far as the posterior margin of the fourth seg- 
ment. In this specimen it is not possible to determine how close 
the anterior parts of the facial sutures are to the anterior margin 
of the cephalon, since they are not clearly differentiated here. 
The state of preservation of the thoracic segments and of the 
pygidium is excellent, and this is the chief reason for presenting 
here a figure of this smaller specimen. In the collections at 
Wilmington College, in Ohio, a cephalon occurs which has a 
length, along its median parts, of 8.5 cm., and a width of 20 
cm. This specimen evidently came from the base of the Liberty 
formation, since the slab contains also columns of Glyptocrinus 
richardsoni Wetherby, which is characteristic of that horizon. • 
Remarks. Both the Huffman Conservancy dam specimen 
and the Roaring Run specimen are characterized by cephalons 
and pygidia which are remarkably short compared with their 
width. This is true also of the Wilmington College specimen. 
Only two species of Isotelus have been described from the 
Richmond formation: Isotelus maximus Locke from the Liberty 
member of the Richmond in Ohio, and Isotelus iowensis (Owen) 
from the Maquoketa member in Iowa. 
Isotelus iowensis is a much smaller species, 10 to 12 cm. long, 
with’ much more elongate cephalons and pygidia, compared 
with their width. 
Isotelus maximus is founded on two specimens found in the 
Liberty member of the Richmond formation a short distance 
above the mouth of Treber’s Run, three-quarters of a mile 
southwest of Duncanville, and 8 miles southwest of Peebles, 
Ohio. Here the, two types were found by Dr. John Locke in a 
strongly rippled layer of limestone, the ripples varying from 2 
to 3 feet in distance from each other, and the troughs varying 
from 2 to 3 inches in depth. Similar rippled layers of lime- 
stone occur at higher elevations up the run. Both of the type 
specimens were figured by Dr. Locke (Geol, Surv. of Ohio, 1838, 
pp. 247-249, figs. 8, 9; see also fig. 1 and 2 on plate XVII of 
this publication), and they are mentioned again in his descrip- 
tion of Isotelus megistos Locke (Amer. Jour. Sci., 42, 1842, p. 
366, pi. 3, fig.). 
