ACTrXOCEEATID^. 
197 
description of the siphuncle, as very little is known ahont the shell. 
Prof. Whitfield thus describes an example of the species belonging 
to the collection of the Geological Survey of Wisconsin : — “ The 
outer shell .... tapers very rapidly, resembling in form a 
species of Gomplioceras, hut it is too imperfect to permit a descrip- 
tion .... The discs are seen occupying the position of the 
ordinary siphuncle within the body of an Orthoceras [Actinoceras\ 
with the true septa and outer shell surrounding it. The discs cor- 
responding in number and position to the septa, and the obliquity 
of the discs to the axis of the series is seen to correspond to the 
eccentricity of their position within the Orthoceras, as is often the 
case with the ordinary siphuncle.” 
The siphuncle is elliptical in section, the ratio of the two dia- 
meters in an uncompressed specimen being as 9 : 8. It has a very 
perceptible curvature, and its rate of increase is a little more than 
1 in 3, measured along the convexity. The distance of the septa 
from each other, as computed by the vertical diameter of the 
siphuncular discs or segments, varies from 2 to 2| lines in a spe- 
cimen measuring 2^ inches along its outer curvature. This same 
specimen has a transverse fissure (fig. 25 A,/) in several of the 
discs, situated a little above the median line, and indicating the 
position of the row of foramina which gave exit to the tuhuli pro- 
ceeding from the endosiphon. The latter is seen in the same 
figure at en. 
Horizon. Niagara Group (Wenlock). 
Locality. Drummond Island, Lake Huron. 
Well represented in the Collection. 
Discosorus remotus, sp. nov. 
1824. Columns composed of circular discs &c., Bigshy, Trans. Geol 
Soc. ser. 2, vol. i. p. 204, pi. xxx. f. 7. 
^p. Char. This species is known only by fragments of the 
siphuncle, hut as these differ in several particulars from the other 
two species of the genus, it seems advisable that it should he sepa- 
rated from them under a distinctive title. The most marked fea- 
ture in which the present species differs from J). conoideus is in the 
distance of the siphuncular segments (or, in other words, of the 
septa) from each other. These are in Z). remotus 2^ lines apart, 
where the diameter of the siphunele is 7 lines ; in B. conoideus, on 
the other hand, the segments are scarcely 2 lines apart at that dia- 
meter. They are also flatter in the present species than they are 
in D. conoideus, and they exhibit the peculiar dual character (one 
