84 



PALEONTOLOGY 



the Discosorus they diminish rapidly towards the last chamber. 

 Perhaps the most remarkable fossil of this group is the Huronia 

 (fig. 20, s), found in the upper Silurian limestone of Drum- 

 mond Island. Siphuncles 6 feet in length and 1$ inch in 

 diameter, were seen by Dr. Bigsby in the cliffs ; they are sili- 

 cified, and stand out in bold relief from the matrix, but are un- 

 accompanied by any vestige of the shell, except in one or two 

 instances, where the septa are faintly indicated by coloured 

 lines. They are sometimes overgrown with coral, and were 



Fig. 20. 



i. Nautiloceras Omalii, de Kon. ; Carboniferous, Belgium. 



2. Lituites (Breynius), U. Silurian, Sweden. 



3. Section of Clymenia, shownng internal siphuncle; Devonian, Petherwin. 



4. Section of Camaroceras duplex, Wahl. ; L. Silurian, Kussia. 



5. Siphuncle of Htironia Bigsbyi, Stokes ; with outline of shell, and septa. 



6. Siphuncle of Discosorus, Hall ; U. Silurian, Lake Huron. 



7. Phragmoceras ventricosum, Sby. ; L. Ludlow rod; Herefordshire. 



8. Gyroceras Eifeliense, d'Arch. ; Devonian, Prussia. 



9. Ascoceras Bohemicum, Barr. ; U. Silurian, Prague. 

 10. Goniatites, Henslowi, Sby. ; Carboniferous, Asturias. 



evidently so durable as to remain on the sea-bed long after the 

 shell itself had decayed. The joints of the siphuncle are 

 swollen at the upper part, and the interior is filled with an 

 irregularly-radiated structure, apparently produced by the 

 plaiting and calcification of the lining membrane. This struc- 



