_ with the succeeding 
294 General Notes. [ March, 
unfortunately the median area of the cephalic shield is wanting. 
The integument is rather thin, showing no traces of segments; 
its surface may have had a few scattered small tubercles, at least 
there are slight indications of them. The surface is smooth and 
shining. 
The cephalic shield is nearly twice as broad as long; the pos- 
terior lateral angle is well-rounded, with no sign of a lateral 
spine; in front the edge was probably obtusely rounded; the 
surface is slightly convex, the disk being low and flat; the hind 
edge of the shield is moderately concave, the limits between it 
and the urosome being clearly indicated by a slight, but distinct, 
regular curvilinear suture. 
The urosome is about three-fourths as long as, but equal in 
width to the cephalic shield. The front edge is somewhat arcu- 
ate, so that the projecting anterior-lateral angle is directed a little 
forward, and is quite free from the lateral angle of the cephalic 
shield, which turns away anteriorly from it, leaving a triangular 
space between the sides of the two regions. Posterior edge of 
the urosome regularly rounded, and with slight margin. No 
traces of a caudal lobe or spine. Total length 20™™' total 
breadth 20™™ length of cephalic shield 11™™* breadth 20™™ i 
length of urosome, 9™™: breadth, 19.5": Collection of R. D. 
Lacoe, 2017 “© in a nodule from Mazon creek, Morris, Illinois. 
This remarkable animal was disk-like in shape, composed of 
two regions, the head and abdomen or urosome, which are more 
distinctly separate than in the Cyclide; yet there are no posi- 
tive characters to separate it from this group, to which we would, 
for the present at least, refer it, as it is orbicular, tailless, and 
a c trias. The mesozoic þeds are not extensive, 
ae but are variously developed. The lower trias, muschelkalk and 
