APPENDIX. 559 



Having requested my friend Mr. Stokes, by whom 

 some of Dr. Bigsby's specimens were described, to ex- 

 amine this part of Captain Back's collection, I have 

 been favoured by him with the following observations ; 

 and I hope that Mr. Stokes himself will soon lay before 

 the Geological Society a paper, accompanied by figures, 

 illustrating the structure of these very interesting fossil 

 remains. 



" Among the limestone fossils brought by Captain 



" Back from Lake Winipeg, are some like those which 



" were obtained by Dr. Richardson from the same 



" locality in the year 1820, but which were not in a 



" state sufficiently perfect to enable us to understand 



" their structure and relations. A memorandum having 



" been given by Dr. Richardson to Captain Back, of 



" the spot from whence the fossils were obtained, 



" the latter has succeeded in procuring several speci- 



" mens, which, although broken, are sufficiently well 



" preserved to illustrate the nature of these remains. 



" They are orthocerata of a peculiar kind, and resemble 



" in their most important points those found at Thes- 



" salon Island in Lake Huron, and described by Dr. 



" Bigsby in the Geological Transactions (Second Series, 



" vol. i. pp. 192. and 195. to 198.). They are, how- 



" ever, probably not of the same species ; but the 



" point of resemblance is the structure of the siphon, 



" which has a tube within it, as described and repre- 



" whole of the States of Ohio, Illinois, Indiana, and Michigan, 

 " and the rest of the Valley of the Mississippi." — (Geol. 

 Trans. 2d Series, vol. i. pp. 188— 191.) See also "Notes 

 " concerning the Geology of North America, from Papers 

 " presented to the Society by the late Earl Selkirk." (Geol. 

 Trans. 1st Series, vol. v. p. 598, &c.) 



