Mr. Stokes on Orthocerata. 889 



Huron* some Orthocerata of peculiar forms are described ; but since 

 the publication of that memoir, Mr. Stokes has received many- 

 other specimens, collected during the expeditions of Sir Edward 

 Parry, Sir John Franklin, the late Capt. Lyon, and Capt. Back, and 

 by Capt. Bayfield during his survey of the lakes and the river St. 

 Lawrence. The object of the present communication is to describe 

 some species indicating generic separations among the Orthocerata, 

 and to call attention to certain considerations respecting the relations 

 of the shells to the animals to which they belonged. 



The first generic distinction adopted by Mr. Stokes consists in a 

 large siphuncule, much dilated in each chamber, and contracted at 

 the parts where the septa are attached to it. Within the siphun- 

 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 Bronnf 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. i2ic7«ffrc?5om7 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 HuroniaX. 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 oflfered some remarks " respecting the relations 

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



• Geological Transactions, 2nd Series, vol. i. p. 195 et seq. Pis. 25 and 26. 



t Letk/ra geognostica, vol. 1. p. 98. tab. i. fig. 8. 1 835. 



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



