689 



cule is a continuous tube which, appears to have been capable of ex- 

 pansion or contraction, and is furnished with radii in verticillations, 

 which connect the tube with the walls of the siphon. For this 

 genus he retains the name of Actinoceras, given by Bronn* to 

 figures 1 — 3, PI. 25, vol. i. N.S. of the Geological Transactions. 

 Four species have been established by Mr. Stokes ; namely, Acti- 

 noceras Lyonii from Igloolik and Ooglit ; A. Bigsbii from Thessalon 

 Island, in Lake Huron; A. Richardsonii from Lake Winipeg; and 

 A. Simmsii from Castle Espie, in the County of Down, Ireland. 



The character of the second genus is a siphunculus, similar in 

 external form to the preceding, but the inner part is divided into 

 portions corresponding in number with the chambers, and deeply 

 indented in the middle, where the -septa of the shell are attached to 

 them ; so that one half of each division of the siphuncule is in one 

 chamber, and the other half in the next chamber. The opening or 

 interior passage is comparatively small, and the inner and outer 

 walls of these divided portions, which are separated by a consider- 

 able space, are beautifully curved. From the resemblance of the 

 siphuncule to a row of beads, Mr. Stokes proposes to call the 

 genus Ormoceras. Three species were described, all of them ob- 

 tained from Drummond Island in Lake Huron ; Ormoceras Bayfieldii, 

 0. Backii, and 0. Whitei. 



Among the fossils noticed in Dr.Bigsby's paper, were several which 

 Mr. Stokes then considered to be corals from the internal plates, and 

 to which he gave the generic name of Huroniaf. He has, however, 

 since discovered, that they do not possess the peculiar, central struc- 

 ture, exhibited by the greater number of the lamelliferous corals ; 

 but that they have a continuous central opening ; and, from the ex- 

 amination of other specimens, he now considers that these bodies are 

 the siphuncules of true Orthocerata. He proposes, nevertheless, to 

 retain the generic name of Huronia ; and has called the only species, 

 yet found with traces of the septa, Huronia Portlockii. 



Mr. Stokes then offered some remarks " respecting the relations 

 of the shell to the animal to which it belonged." From the si- 

 phuncule being so often preserved without the external portion of 

 the shell, and the latter, including the septa, being, when retained, 

 extremely thin, he is of opinion that the shell must have been en- 

 veloped in the animal to protect it from injury. .This view of the 

 relation of the shell to the soft portions of the creature, he is of 

 opinion, receives confirmation from his having observed only one 

 instance of a parasitic body being attached to Orthocerata. In this 

 instance, indeed, there are evidences that the parasite, a coral, must 

 have been formed after the death of the animal of the shell {Actino- 

 ceras Simmsii), for the specimen exhibits in some parts, layers of 

 earthy matter, alternating with layers of the coral ; and, therefore, 

 the growth of the latter must have been more than once inter- 

 rupted by the deposition of sediment. The memoir concluded with 



* Lethaa geognostica, vol, i. p, 98. tab. i. fig. 8. 1835. 



t Geological Transactions, 2nd Series, vol. i. p. 202, PI. 28, 



