Remarks on the Trilohite. 37 



being reflected beneath the animal so as to form a flat horizontal 

 plane, which terminates in a kind of lunate spine, the horns of 

 the crescent being curved towards each other. These horns are 

 six lines in length, and their points are sharp and translucent. 

 We have received from Dr. Warder a specimen of this singular 

 structure, which was found, with other fragments of the isotelus, 

 near Springfield in Ohio. Although it lies on the rock, unaccom- 

 panied by any other fragment of the animal, its exact resemblance 

 to the figure given by Dr. Dekay leaves no doubt thai it once 

 belonged to an isotelus. Among other conjectures respecting the 

 uses of this crescent-shaped structure, it is observed that when 

 the animal was attacked " it may roll itself up into a ball, as 

 indeed it is often found, and by some mechanism these processes 

 may be inserted into the corresponding cavities in the tail, and 

 thus retain permanently a rolled position, presenting nothing but 

 its calcareous covering to the enemy : or they may supply the 

 place of antennae, for which their form and contiguity to the 

 mouth and brain would seem to render them peculiarly applica- 

 ble." The first conjecture above noticed was ingenious, and will 

 no doubt be confirmed when the lower surface of the tail is dis- 

 covered. The inferior organization of the calymene bufo has at 

 any rate given great plausibility to this opinion. 



We have also carefully examined another fragment represent- 

 ing a similar structure. The original fossil was found in Ohio, 

 and is now in the possession of W. Wagner, Esq. of Philadel- 

 phia. The rock on which it occurs is a gray limestone full of 

 other petrifactions. This lunate structure difl^ers essentially from 

 the one noticed by Dr. Dekay ; the points of the crescent are 

 rounded and do not curve towards each other ; the terminations 

 are not raised and translucent, but the v/hole surface is nearly 

 flat. It however formed, undoubtedly, a portion of the under 

 surface of some trilobite, whether that of an asaphus, an isotelus, 

 or a dipleura, we are unable now to determine. In the Geol. 

 Trans., No. 8, Vol. I, pi. 27, there is a figure by Mr. Stokes of 

 what is said to be the under surface of the anterior portion of the 

 shield of an asaphus platycephalus from Lake Huron. Dr. Buck- 

 land, whose copy of the figure we have only seen, observes con- 

 cerning it, that the entrance to the stomach of the animal was 

 between these lunate processes " analogous to that in recent 

 crabs." The A. pJiatycephahis is synonymous with /. gigas of 



