8 
contraction. The cone development, therefore, appears to be stout- 
whorled serpenticone to about sphaerocone to part ellipticone and part 
contracticone. Yakounoceras differs from Seymourites in having a simpler 
and less deeply cut suture line, a shorter, yet distinct, accessory lobe on 
the inner side of ES, LI equal in length to EL, not longer than, and, on the 
whole, deeper saddles and narrower and longer lobes. The genotype is 
Yakounoceras gitinsi McLearn. 
It differs from the tuberculate genera Gowericeras S. Buckman; 1 Gali - 
laeanus S. Buckman, 2 and Galilaeiceras S. Buckman 3 in having LI equal 
to, not shorter than, EL. The well-defined, although short, accessory 
lobe in ES is also a distinction as compared with these genera. The some- 
what narrow long lobes recall Gowericeras , but those of Yakounoceras are 
even longer and are more developed; the accessory lobe is well defined, 
whereas in Gowericeras it is scarcely perceptible; 4 moreover, Gowericeras 
has not the abrupt umbilical enlargement on the ultimate whorl. Keppler- 
ites Neumayr and Uhlig 5 and Ammonites macrocephalus evolutus Quenstedt 6 
differ in not retaining the tubercles. The latter has also a very different 
suture line with shallower saddles and lobes much shorter and wider. 
Yakounoceras gitinsi McLearn 
( Gitins , Indian name of the Eagle clan) 
Plate III, figure 1; Plate IV, figure 1; Plate VIII, figure 5 
1927. Yakounoceras gitinsi McLearn, Trans. Roy. Soc., Canada, 3rd ser., 
vol. 21, sec. IV, p. 72, PI. 1, fig. 2. 
Diameter 138-0 105-0 
Height, whorl 30-5 44-7 
Thickness, whorl 33-0 46-5 
Width, umbilicus 32-0 23-5 
The second measurement is taken just a little beyond the point of 
umbilical enlargement and the first about one-fourth whorl back from the 
anterior end of the ultimate whorl. The former corresponds in position 
to the anterior measurement given for Seymourites plenus McLearn, and to 
the measurement given for *S. multus } i.e. at the maximum diameter. 
In S. gitinsi the outer whorl extends beyond this stage and bends back, 
so that the diameter at the aperture, 133 mm., is less than the maximum 
diameter of this ellipticonic shell. The umbilical enlargement and eccent- 
rumbilication begin at a diameter of about 100 mm. There is about three- 
fourths of a whorl of living chamber, the anterior part of which is con- 
tracted. The primary angular ribs end in small tubercles, from each of 
which branch 3 narrow, elevated, secondary ribs, inclined a little on the 
sides, but straight across the venter. In addition there are single inter- 
calated ribs. There are 33 primary and about 130 secondary ribs on the 
ultimate whorl, or about the same number as in S. plenus. ES is deep and 
unequally divided by a narrow lobule on its inner side. EL and LI are 
long and narrow and about equal in length. 
1 Type Ammonites, III, pt. 29, PI. 254 (1921). 
* Type Ammonites, IV, pt. 32, PI. 293 (1922). 
* Type Ammonites, IV, pt. 32, PI. 290 (1922). 
1 Buckman, S. S. : personal communication. 
8 See Buckman, S. S.: Type Ammonites, IV, pt. 32, PI. 289A (1922). 
* Amin ;n. Schwab. Jura, p. 655, PI. 77, figs. 1-5 (1887). 
