706 Mr. Stokes on Orthocerata. 



sists in the structure of the siphuncle, which had, I believe, never been noticed 

 till it was described in Dr. Bigsby's paper. 



The siphuncle is large in proportion to the shell, and has a tube which runs 

 through its whole length, setting off radii in verticillations from the outside 

 of the tube to the inner wall of the siphuncle. These verticillations corre- 

 spond in number to the chambers of the shell. 



The late Capt. Lyon collected at Igloolik, where the expedition under Sir 

 Edward Parry passed the winter of 1822-23, some Orthocerata which pre- 

 sent a similar large-sized siphuncle and a small internal tube, but no traces of 

 the radii connecting the tube with the walls of the siphuncle can be seen. In 

 these, however, the condition of the specimens, in which the siphuncle is 

 filled with crystals of carbonate of lime, prevents a positive conclusion that 

 the radii did not exist. Similar ones were found by Capt. Nias at Oog-lit. 



Among the specimens brought by Dr. Richardson from Lake Winipeg 

 were some fragments of Orthocerata which exhibited a tube within a similarly 

 large siphuncle, but the specimens were not sufficiently perfect for descrip- 

 tion, and additional information was the more requisite because this inner tube 

 was surrounded by numerous radiating plates which filled up the remainder 

 of the siphuncle. Other specimens of different sizes so much resembled the 

 siphuncles of the preceding, that it was not possible to doubt their identity 

 of character, although no traces of septa were visible; and at the same time 

 they presented so much agreement in structure with the fossils found at 

 Drummond Island in Lake Huron, which 1 described in Dr. Bigsby's paper 

 as corals, under the name of Huron iae, as to lead to a belief that the latter 

 also were siphuncles of Orthocerata which had been entirely separated from 

 the septa and external shell. To clear up, if possible, a point so interesting 

 to those who study fossils was most desirable, and when Capt. Back was about 

 to undertake the expedition in search of Capt. Ross's party in J 832, Dr. Ri- 

 chardson furnished him with a memorandum of the particular locality of Lake 

 Winipeg, in which the fossils were found, with a request that he would seek 

 for better specimens. 



Capt. Back succeeded in obtaining some which have added much to our 

 knowledge of the subject, and with further evidence which will be presently 

 noticed, I think that the connexion of all these bodies with the family of Or- 

 thocerata is established. 



In the month of March last, Capt. Dawson, R.E., called my attention to a 

 large specimen of an Orthoceras found at Castle Espie, in the county of Down, 

 in Ireland, by Mr. Frederick W. Simms. On examination, I found in it the 

 same peculiarities of the tube within the siphuncle, and radii from the tube. 



