710 Mr. Stokes on Orthocerata. 



I have since observed, that the hard parts are peculiarly contorted, generally 

 in a spiral manner, for the purpose of giving a stronger attachment to the base 

 of the animal's stomach, as is described in the Zoological Journal, vol. iii. 

 p. 486. 



The centre of the Huroniae is different from this, as in a longitudinal section 

 an opening or tube is seen to pass continuously through the whole length. 



Other specimens, which could not be separated in character from the si- 

 phuncle of the Actinoceras Richardsoni from Lake Winipeg, but on which 

 no traces of septa, or external shell, could be perceived, had, as before ob- 

 served, so much resemblance to the Huroniae, as to lead to the conclusion that 

 the latter also were siphuncles of Orthocerata ; but if so, we have to account 

 for the constant disappearance, in the Huroniae, of all traces of the septa and 

 of the external shell. 



This extraordinary fact seems to be intelligible only on the supposition that 

 these parts were extremely thin, or composed of a substance not sufficiently 

 strong to be permanent after the death of the animal. A strong corrobora- 

 tion of this suggestion is furnished by a specimen from Drummond Island, 

 given to me by my friend Captain Portlock, R. E., President of the Geolo- 

 gical Society of Dublin. A very careful drawing of this specimen is given in 

 PI. LX., fig. 5. The lines on this specimen, it cannot, I think, be doubted, 

 indicate the septa and external shell of an Orthoceras, while enough of the 

 siphuncle is seen to establish its connexion with the Huroniae. These lines 

 show that the substance of the external shell and of the septa must have 

 been so thin that it is not a matter of surprise that they have been very rarely 

 preserved. 



To this specimen I have given the name of Huronia Portlockii, as I do not 

 at present propose to alter the name of the genus. 



To add to the evidence on this subject, 1 caused longitudinal sections to be 

 made of some specimens of Huroniae, two of which are represented in PI. LX., 

 fig. 2 and 3. They are of different forms, approaching to the H. vertebralis 

 and H. spheroidalis of Dr. Bigsby's paper before quoted. These fossils are not 

 in the most favourable state of preservation for giving clear evidence of their 

 original structure : the calcedony and quartz, which has crystallized upon it, 

 tend much to make it obscure. Notwithstanding this, there is to be traced a 

 great resemblance to the structure of the interior of the siphuncle of the Or- 

 moceras ; in each of them may be observed parts so greatly resembling the 

 beautifully curved portions figured in O. Bayfieldii, and so constantly to be 

 traced in each enlarged portion of the fossil, that it seems evident that they 

 indicate the original structure. 



