8 OLAF HOLTEDAHL. M.-N. KI. 
infer the outer boundaries of the shell, and it is then possible to arrive at 
a satisfactory conclusion. 
Actinoceras beloitense WHITFIELD. 
Plate IV, Fig. 2. 
1877. Orthoceras (Actinoceras) beloitense N'nrrrrELD, Ann. Report Geol. Survey of Wisconsin, 
pag. 79. 
1882. Orthoceras (Actinoceras) beloitense WHITFIELD. Geol. of Wisconsin, Vol, IV, p. 226. 
AE ne EID ere fig. 9, ro. 
1897 Actinoceras beloitense CLARKE. Geol. of Minnesota. Vol. III, part ll p' 76° El 
XLVII, fig. 18. 
A number of weathered interiors occur of this form, of which the most 
instructive is shown on pl. IV, fig. 2. We here see somewhat plainly the 
form of the siphuncle, and its comparatively small size which is one of the 
special characteristics of this species. We can also observe the endosi- 
phon and notice the connection between the latter and the outer siphonal 
wall by filaments. 
The exact outer form of this species has not been observed from any 
of the specimens, although it is possible to recognise the oval section, 
and the eccentric situation of the siphuncle. The greatest breadth of the 
shell measured 7 cms. 
Actinoceras beloitense has been found in the Buff beds of Wisconsin. 
Actinoceras sp. 
PL IID Ei 2. 
One form which in certain details differs from the one described above, 
although it cannot with certainty be referred to another species is shown 
here. It exhibits a comparatively thicker siphuncle. The breadth amounts 
to about + of the diameter of the shell, whilst in A. beloitense the condi- 
tions were 1—1. In addition the septa are much more concave. 
The form approaches the Ordovicic A. tenuifilum Hatt and A. bigsbyi 
HarL, although the agreement is not entire. Both exhibit an even thicker 
siphuncle, with more separated septa and as regards the former also con- 
siderably flatter. 
Of the numerous specimens of orthoceracones showing only the outer 
shape, we have one large straight form, greatly annulated, representing a 
species that occurs frequently (see pl. IV, fig. 1). This shows in size, 
in the position of the septa and the annulations, a great likeness to Cyclen- 
