72 



contracted attitude, and is somewhat distorted. We 

 have given, however, models of the head and the tail, 

 in two distinct pieces. The external shell, or calca- 

 reous covering, is more perfect in this specimen 

 than in any other we have ever seen. A considera- 

 ble portion of the under side of the anterior part of 

 the buckler, is also well preserved, and perfectly co- 

 incides with the figure and description given of it by 

 Dr. Dekay and Mr. Stokes. There is another frag- 

 ment of an Isotelus in the cabinet of Mr. Wetherill, 

 showing eight articulations of the abdomen, which 

 probably belongs to another individual of this spe- 

 cies. The dorsal shell is in a high state of preser- 

 vation. This species is embedded in clay slate, and 

 was found in Newport, Kentucky. 



GENUS CRYPTOLITHUS. Green. 



Among the numerous organic relics embedded 

 in black limestone at Trenton Falls, in the State of 

 New York, there is often found the fragment of a tri- 

 lobite which cannot properly be referred to any of 

 the genera already mentioned. Dr. J. Bigsby, in his 

 Sketch of the Geology of the Island of Montreal, has 

 figured and described a fossil which occurs at that 

 place, which approaches in its specific characters to 

 the fragments found at Trenton but he does not 

 suggest for his relic any name. Professor Brong- 

 niart has also represented, plate 4, figs. 5 and 7 A. 

 B. C., the fragments of trilobites from Russia and 

 from Llandillo, in Wales, which seem to differ but 



