Fig. 5. Protocycloceras cf. lamarcM (Billings). A natural vertical section 
exposing the siphuncle, apparently with invaginating septal necks. Figures 5A 
and 5B on Plate 33 represent a cross-section and a vertical section of this speci- 
men, as far as can be determined from the part preserved. From Bear Island; in 
the younger dolomite division of the Heclahook system, regarded as of Canadian 
age. In the Palaeontologisk Museum, Kristiania; collected by Dr. Olaf Holte- 
dahl in July, 1918. Original of fig. 1 on Plate XIII on HoltedahPs paper ‘‘On 
the Paleozoic Series of Bear Island,’’ 1919. 
Fig. 6. Deltoceras (?) sp. A section lengthwise through the siphuncle and 
parallel to the dorso-ventral diameter, exposing the outline of the septa; triangu- 
larly limited by two oblique sections, of which the lower one is margined by a 
second septum, while the upper oblique section exposes only the ventral part of 
a third septum. Figures 6A and 6B Plate 33 represent the same specimen, 
the first in its present condition, the second with an attempt at restoration, the 
missing parts being indicated by dotted lines. Figure 6(7 on the same plate is 
a cross-section of the specimen. From Bear Island; in the younger dolomite 
series of the Heclahook system, regarded as of Canadian age. In the Palaeon- 
tologisk Museum, Kristiania; collected by Dr. Olaf Holtedahl in July, 1918. 
Figure 2 on Plate XIII of HoltedahPs paper “On the Paleozoic Series of Bear 
Island,” is a direct view of the septum at the base of the specimen, before this 
specimen was sectioned. 
Fig. 7. Actinoceras sp. A vertical section passing in a lateral direction through 
the siphuncle ; along the lower half of the specimen the exposure is due to weather- 
ing, along its upper half the weathered surface has been ground off sufficiently 
to expose the outlines of the annulations of the siphuncle. Along the center 
of the siphuncle is the heavy strand-like deposit characteristic of numerous 
species of Actinoceras . Figure 2 on Plate 32 is an attempt at a cross-section of 
this specimen, suggesting that its siphuncle was small compared with the diameter 
of the conch. From some unknown locality either on Boothia Felix or on King 
William Land ; probably from the Black River limestone. In the Palaeontologisk 
Museum, Kristiania; collected by Lieut. Godfred Hansen in 1903-04. Original 
of Fig. 2 on Plate III of HoltedahPs paper “On Some Ordovician Fossils from 
Boothia Felix and King William Land,” 1912, however, since the publication of 
HoltedahPs paper the matrix has been ground away from the left side of the 
specimen in an attempt to get some idea of the original size of the conch. 
PLATE XXVIII 
Fig. 1. Actinoceras tenuifduyn centrale Var. nov. A vertical section through 
the center of the siphuncle. The apparent narrowing of the siphuncle at the 
top of the specimen is due to oblique weathering. The axial part of the siphuncle 
is occupied by an irregular tube filled by dark matrix; this is exposed by weather- 
ing at the top of the specimen and is glimpsed through the calcareous deposit 
in the lower part of the specimen. There also are traces of the tubuli which 
radiate from this axial part toward the annular segments of the siphuncle. 
Figure 4, on Plate 32 is a cross-section of the same specimen. From the Black 
River limestone at Watertown, New York. Received from Dr. Rudolf Ruede- 
mann of the New York State Museum of Natural History. 
Fig. 2. Actinoceras tenuifilum (Hall). A vertical section through the center 
of the siphuncle, tha latter narrowing toward the top. In the upper part of 
the specimen the axial part of the specimen was still comparatively open before 
