A. H. Foord—The Genus Actinoceras. 487 
Tasie III.— Central and South-West Europe. 
CENTRAL Monvacne Noire Tenapvon 
BELGIUM. SPAIN. ° 
Europe. S.E. FRANCE. ea SARDINIA. 
( Up. Cambrian Olenus Dictyo- Olenus ? 
or (Hof) nema 
Olenus zones. 
Mid. Cambrian | Paradoxides Unknown | Paradoxides |Paradoxides 
4 or Para- | (Bohemia) 
‘ doxides zones. 
Low. Cambrian Unknown Unknown Unknown Unknown 
or 
{| Olenellus zones 
CAMBRIAN SYSTEM. 
Paradoxides and 
Archeocyathus fauna, 
i 
IIJ.—Nots on tHE Genus Acrivoceras, WITH ParTicULAR REFERENCE 
TO SPECIMENS IN THE British Museum, SHOWING THE PERFORATED 
APEX OF THE SIPHUNCLE. 
By Antuur H. Foorp, F.G.S. 
HE genus Actinoceras was founded by Bronn in 1887,’ upon Dr. 
Bigsby’s figures in the Transactions of the Geological Society ;* 
the chief distinguishing character being the possession of a large, 
dilated, and segmented siphuncle, filled with radiating deposits. 
The presence of a smaller internal tube with tubuli radiating there- 
from and communicating with the septal chambers through the wall 
of the siphuncle, had not then been observed. 
Fig. 1. 
mM RR Ce, SSS, 
Fic. 1. Weathered fragment of Actinoceras Bigsbyi, showing the endosiphon, en, 
with some of its tubuli, ¢ (thickened by incrustations of pearl-spar), s, septa. 
Nat. size. From the Black River Formation of Thessalon Island, Lake Huron. 
Fic. 2. Fragment of the same species, showing the foramina, /, in the walls of the 
siphuncle, by which the tubuli thrown out by the endosiphon may have com- 
municated with the septal chambers; s, septa. Natural size. From the 
Cincinnati Group, Versailles, Kentucky. 
1 Tethea Geognostica, Zweite Aufl, Band i. p. 97. 
2 Ser. 2, vol. i. 1824, p. 198, pl. xxv. figs. 1, 2 (excl. fig. 3). 
