13 
T . runcinatum S. Buckman 1 has a much smaller umbilicus. T. subro - 
tundum S. Buckman 2 among other differences is increasing in thickness of 
whorl on the outer whorl and has more ribs. 
Horizon and Locality. Collected by Dr. C. F. Newcombe in 1895 
on the south side of Alliford bay, probably from the sandstone bed near the 
top of the Yakoun formation. 
Type. National Museum of Canada, Ottawa; holotype, Cat. No. 
5990. 
Family, sphaeroceratidae S. Buckman 
Genus, Defonticeras McLearn 
1927. Defonticeras McLearn, Trans. Roy. Soc., Canada, 3rd ser., vol. 21, 
sec. IV, p. 72. 
Inner whorls and posterior part of ultimate whorl sphaeroconic, with 
very small umbilicus, followed by marked and abrupt umbilical enlargement 
on the anterior half of the ultimate whorl. Mouth border rather simple, 
having behind the lip a well-defined sulcus and in some species a ridge of 
low relief. Living chamber is about three-fourths of a whorl or less. 
Primary ribs are fairly stout and slightly inclined, but not sloping well 
forwards at the anterior end of the ultimate whorl. The secondary ribs 
are straight across the ventral area. No tubercles. The suture line is 
complex with a wide L2 and very small S2 and auxiliaries. The point of 
furcation of the ribs is on the outer part of L2. 
The genotype is Defonticeras defontii McLearn. 
Chondroceras Mascke 3 has a three-ridged mouth, a somewhat regular 
umbilicus, and fine ribs sloping well forward near the anterior end of the 
ultimate whorl. 4 The stout ribs recall Emileia S. Buckman, but the suture 
line is simpler and there are other differences. 
Defonticeras defontii McLearn 
Plate XII, figures 1-3 
1927. Defonticeras defontii McLearn, Trans. Roy. Soc., Canada, 3rd ser., 
vol. 21, sec. IV, p. 72, PL 1, fig. 3. 
(a) 
(b) 
(c) 
Diameter 
62-4 
58-5 
451 
Height, whorl 
40-0 
46-8 
52-5 
Thickness, whorl. 
62-3 
780 
Width, umbilicus 
22-4 
15-3 
(a) is taken about one-sixth of a whorl back from the anterior end of 
the ultimate whorl, (b) is taken one-third of a whorl back, and (c) is taken 
at the beginning of the ultimate whorl. This species has very stout whorls, 
both thick and high. The sides are somewhat flattened and the venter is 
broad and arched. There is nearly five-eighths of a whorl of living chamber. 
The ventral part of the aperture is broken off. The umbilical enlargement 
is abrupt and comes at the beginning of the last half of the ultimate whorl. 
There is also whorl contraction. The whorls are ornamented on the sides 
with slightly inclined primary ribs which rapidly increase in size and spacing 
1 Type Ammonites, pt. 34, PI. 318 (1922). 
J Type Ammonites, pt. 34, PI. 319 (1922). 
* Die Stephanoeeras — Verwandten in den Coronatenschichten von Norddeutschland, Gottingen, 1907. 
4 Buckman, S. S.: personal communication. 
