NIAGARAN CEPHALOPODS 
299 
they were empty. Hall in the reference to D. conoideus, cited 
above, mentions similarly included remains. 
These siphuncles evidently belonged to some ovoid hrevicone 
t 3 rpe of cephalopod. In the university collection is a fragment 
of a cast of a conch with part of the siphuncle in place. The 
siphuncle is broken in such a way that.it can not be referred to 
this species with absolute certainty but the following points can 
be seen clearly; seven camerae are present on the antisiphonal 
side ; the sutures undulate slightly ; the uninjured surface of the 
specimen preserves impressions of longitudinal ridges; the sur- 
face along these ridges is a gently convex curve ; the siphuncle is 
nummuloidal and tapers in both directions. 
This species is referred to the genus Discosorus with some doubt. 
Many fragments of siphuncles in the collection taper in one direction 
only; these conform to Hall’s description of the genus as given in the 
reference cited at the head of this description, but a redefinition of the 
genus is necessary in order to include biconoid or doubly tapering 
siphuncles. 
The specific name is also offered with some hesitation, for it may be 
possible that the siphuncles at hand are but more complete specimens 
of Hall’s D. conoideus. However, it seems unlikely that good observers 
like Bigsby, Hall, Whitfield, Barrande, Hyatt and others should have 
failed to notice biconoid forms or at least to have suspected the biconoid 
character of the siphuncle if such was originally the complete form of 
the specimens they studied. 
Occurrence and Locality : Occur as dolomitic casts in the 
Niagaran at Maquoketa, Jackson county, and also at Hopkinton 
and vicinity in Delaware county, Iowa. One silicified specimen 
is labelled Niagaran, Delaware county. State University collec- 
tion. 
Actinoceras cf. richardsoni Stokes. 
Plate XXXIV, figure 3. 
1840. Actinoceras richardsoni Stokes. Trans. Geo. Soc. London, second 
series, Vol. v, pt. ii, p. 708, PI. lix, figs. 2, 3. 
Siphuncle nummuloidal, straight, round in cross section; the 
fragment at hand shows little or no tapering. 
Segments discoidal, outer edges evenly rounded, surface of 
upper half curved more abruptly than the lower to which frag- 
ments of the septa still adhere as in H. turbinaia. The obliquity 
of the segments makes an angle of 105° with the vertical axis. 
The internal characters of the siphuncle are wholly obscured 
by excessive silicification. 
