9 
This species has thinner whorls than Seymourites plenus, S. loganianus, 
or S. multus, and lower whorls than S. plenus or S . loganianus. The 
umbilicus is larger than that of S. plenus or S. loganianus. 
Horizon and Locality. In a sandstone bed near the top of the Yakoun 
formation on the northeast shore of Maude island. 
Type. National Museum of Canada, Ottawa; holotvpe, Cat. No. 
9002. 
Yakounoceras abruptum n. sp. 
(i abruptus , sudden) 
Plate Y, figure 1; Plate VI, figures 1, 2 
Diameter 
121-0 
96-0 
Height, whorl 
34-7 
46-6 
Thickness, whorl 
44-2 
56-6 
Width, umbilicus 
31*5 
14-6 
The second measurement is taken at the point of umbilical enlargement 
and the first at about the anterior end of the ultimate whorl preserved. 
In size this species is between Yakounoceras gitinsi and Yr. ingrahami 
and smaller than the three species of Seymourites described above. It has 
relatively thicker whorls than Yakounoceras gitinsi. The umbilicus of 
the anterior part of the penultimate and posterior part of the outer or 
ultimate whorl is smaller than that of any of the above species, but the 
umbilical enlargement on the anterior part of the ultimate whorl is more 
marked and abrupt. There is about one-half whorl of living chamber 
preserved. There is some whorl contraction on the anterior part of the 
ultimate whorl. Three secondary ribs branch from the small tubercle at 
the end of each primary and there are in addition intercalated secondary 
ribs. The primaries number about 35 and the secondaries 120 on the 
ultimate whorl. 
The inner whorls are much distorted, but dissection of the interior, 
at some cost to the specimen, reveals a runcinate venter at a diameter of 
15 mm. There appears to be less involution and some umbilical con- 
traction in the inner whorls up to the stage of the anterior part of the 
penultimate whorl, with change in cone shape from approximate stout 
whorled serpenticone to about sphaerocone. 
ES is very deep and as in other species of the genus is somewhat 
unequally divided by an accessory lobe on the inner side. EL is about 
equal in length to LI. 
Horizo7i and Locality. In a sandstone bed near the top of the Yakoun 
formation on the northeast shore of Maude island. 
Type. National Museum of Canada, Ottawa; holotype, Cat. No. 
9003. 
Yakounoceras ingrahami n. sp. 
Plate VII, figures 1, 2 
Diameter 
105-0 
78-3 
Height, whorl 
35-0 
46-0 
Thickness, whorl 
44-6 
57-3 
Width, umbilicus 
33-0 
