444 ^rofs Hall on a New Crustaeean. 



described an animal which I have found, or I have found the ani- 

 mal corresponding to your description. I will leave you and the 

 scientific world to judge of the facts. However, after what you 

 have written, I cannot now publish what I communicated to the 

 Albany Institute last winter, without referring to your paper, and 

 in the mean time you may lay this note before the Montreal Na- 

 tural History Society, and publish it, or such parts of it, as you 

 please. 



In February last, I communicated to the Albany Institute a notice 

 of a new crustacean from the Potsdam sandstone of Wisconsin, 

 and subsequently I sent a drawing of the same to M. Barrande. 

 In 1855, I obtained from the Potsdam sandstone of the upper 

 Mississippi River, a fragment of what appeared to be a spine of a 

 crustacean, of very remarkable and peculiar structure, reminding 

 one of that of bone ; and which might at one time, before we 

 had accustomed ourselves to limit the geological range of fishes, 

 have been taken for an ichthyic remain. 



This fragment remained in my collection a subject of much in- 

 terest, for I was aware from its structure that it could belong to 

 no genus of Trilobites, but at the same time I did not think it 

 worth while to publish any notice of it from its incompleteness. 



In 1851, Mr. Daniels, of the Geological Survey of Wisconsin, 

 discovered in the Potsdam sandstone of Black River, in that State, 

 tracks similar to those described by Sir W. E. Logan, in the sand- 

 stone of Canada. This added a new interest to the unknown crus- 

 tacean fragment; and in 1860 I visited the Black River region, 

 to procure if possible some of these impressions. I failed how- 

 ever in finding the precise locality ; and in 1862 sent my assis- 

 tant in the Wisconsin survey, Mr. Hale, to make farther explora- 

 tions, but he did not succeed in finding anything of interest. At 

 another locality however, he obtained some fragments of the crus- 

 tacean before mentioned, among which are two cephalic shields 

 suflSciently perfect to be characterized. I inclose you a drawing of 

 one of these. 



The relations to Limulus are at once suggested by the form 

 and expression of these carapaces, while the large prominent eye- 

 tubercles hold relatively the same position as the small approxi- 

 mate oculiform tubercles or spots on the anterior part of the 

 shield in Limulus, (and also in Eurypterus), The carapace is 

 proportionally flatter than in Limulus ; and has, like that, a strong 



