5 
are probably as in Yakounoceras MeLearn. Runeinate venter not observed 
and if present must be suppressed before the stage of growth of the 
penultimate whorl. The ribs are numerous, narrow, and elevated. There 
is a single row of small, lateral tubercles. The suture line is florid; LI is 
narrow, has a long terminal lobule, and is longer than EL; L2 is shorter 
than LI and more leaf-like; ES is unequally divided by a very long accessory 
lobe, situated on its inner side so that the inner branch is the smaller. 
The genotype is Ammonites loganianus Whiteaves. 
In the tuberculate genera Galilaeanus S. Buckman 1 , Gowericeras S. 
Buckman 2 , and Galilaeiceras S. Buckman 3 , EL is longer 4 , not shorter, than 
LI. These genera also have not so florid a suture line and have not a long 
prominent accessory lobe on the inner part of ES. Galilaeanus is probably 
the most closely related, having similar shallow saddles. Kepplerites 
Neumayr and Uhlig 5 does not retain the tubercles and has not so deeply 
cut a suture line. The tubercles also are not retained in Ammonites 
maerocephalus evolutus Quenstedt 6 and ite suture line is not so deeply cut, 
has not a long accessory lobe in ES, and has a wider and shorter LI as 
compared with EL. 
Seymourites plenus (MeLearn) 
( plenus , full) 
Plate I, figure 1; Plate II, figures 1, 2 
1927. Yakounites plenus MeLearn, Trans. Roy. Soc., Canada, 3rd ser., 
vol. 21, sec. IV, p. 71, PI. 1, fig. 1. 
Diameter. 
154*0 
117*0 
Height, whorl 
40*5 
50*0 
Thickness, whorl 
40*5 
57*4 
Width, umbilicus 
24*8 
18*5 
The first measurement is made near the anterior end of the ultimate 
whorl and the second at the point of umbilical enlargement. The posterior 
part of the ultimate whorl is involute, being subangustumbilicate, has 
somewhat convergent sides outside the tubercles, is broad and rounded on 
the venter, is stout, being both thick and high, and a little thicker than 
high. Umbilical enlargement begins at a diameter of about 117 mm. or 
at about the beginning of the anterior half of the ultimate whorl, where the 
whorl suture passes from inside the tubercles to outside them. The 
proportional height and thickness both decrease on the anterior part of the 
ultimate whorl and are about equal near the aperture. There is a little 
more than half a whorl of living chamber. The primary ribs are angular, 
reclined a little on the inner margin, inclined a little on the inner area, and 
end in small tubercles. There are about 4 secondary ribs to each primary; 
all 4 branch from the primary or 3 branch from it and 1 is intercalated. 
All secondary ribs are narrow and elevated, i.e. plate-like, are inclined on 
the sides, are straight across the venter, are septate on the anterior half of 
1 Type Ammonites, IV, pt. 32, PI. 293 (1922). See also VI, pp. 16-23 (1926). 
s Type Ammonites, III, pt. 29, PI. 254 (1921). 
1 Type Ammonites, IV, pt. 32, PI. 290 (1922). 
1 Buckman, S. 8.: personal communication. 
6 See Buckman, S. S.: Type Ammonites, IV, pt. 32, PI. 289A (1922). The writer has not access to the original 
description of this genus. 
8 Ammon, Schwab. Jura, p. 655, PI. 77, figs. 1-5 (1887). 
