6 
the ultimate whorl, and are separated by flat interspaces wider than the 
ribs T The total number of primary ribs on the ultimate whorl is 33, and 
that of the secondary ribs 135. 
The suture line is deeply cut and florid. ES is very little deeper than 
wide and is unequally divided by a long lobule, which is longer than half 
the depth of ES, and is situated on the inner side, so that the inner branch 
is the smaller. SI is smaller than ES, is hardly as deep as wide, and is 
divided by a long lobule. S2 is much smaller than SI, is wider than deep, 
and is about equally divided by a relatively long lobule and has its inner 
branch on the umbilical margin. EL is longer than wide. Ll is longer 
than EL, is narrower, and has a long, median lobule. L2 is short and 
relatively wider than Ll. All the saddles are much wider than the lobes. 
The tubercle is on the inner border of SI. 
This species at the same stage of growth is somewhat larger and has 
relatively stouter whorls and somewhat smaller umbilicus than Seymourites 
loganianus (Whiteaves). The ornament is similar in both species. What 
is known of the suture line of S. loganianus is similar to that of S . plenus. 
However, S. loganianus is based on an imperfect and distorted specimen 
with which exact comparison cannot be made. 
Horizon and Locality. In a sandstone bed in the upper part of the 
Yakoun formation on the northeast shore of Maude island. 
Type. National Museum of Canada, Ottawa; holotype, Cat. No. 
9000. 
Seymourites loganianus (Whiteaves) 
1876. Ammonites loganianus Whiteaves (part), Geol. Surv., Canada, 
Mes. Foss., I, pt. 1, p. 27, PL 8, fig. 2 only. 
1884. Olcostephanus loganianus Whiteaves (part), Geol. Surv., Canada, 
Mes. Foss., I, pt. 3, p. 211, not PI. 23, figs. 1, la. 
1900. Olcostephanus loganianus Whiteaves (part), Geol. Surv., Canada, 
Mes. Foss., I, pt. 4, p. 276. 
Diameter 136-0 
Height, whorl 40-8 
Thickness, whorl 40-4 
Width, umbilicus. 26-5 
The holotype of this species is too imperfect and distorted to admit of 
exact measurement. The above measurements are only approximate and 
have been made about midway between the point of umbilical enlargement 
and the anterior end of the specimen, at the only place where direct measure- 
ment of the diameter is possible. The anterior part of the penultimate 
whorl has a small umbilicus. There is marked umbilical enlargement on 
the anterior part of the ultimate whorl. The whorls are fairly stout and 
have somewhat convergent sides ventral to the tubercles, but are broad 
and rounded on the venter. The primary ribs are angular, straight, and 
inclined on the sides, outside the inner margin, and end in tubercles. 
From each tubercle there branch 3 or 4 secondary ribs and there are some 
intercalated secondary ribs. The secondary ribs are narrow, elevated, and 
inclined a little on the sides, but are straight across the venter. A part of 
the ES has been prepared with some difficulty; it is deeply cut and has a 
long accessory lobe on its inner side. 
