9 
Sphaerocone of stout Maerocephalitid aspect, rounded ribs of some- 
what low relief, primaries curved, beginning at line of contact and running 
over a convex, indistinctly defined inner margin; secondary ribs arise from 
primaries, partly as bifurcates, partly as intercalates, they fall back some- 
what from line of primaries and have a general versiradiate direction: they 
pass quite straight over venter. The rather small umbilicus is gradate, the 
chord of the convex wall is what is usually called perpendicular, that is at 
right angles to the median plane of the conch: it does not fall outwards to 
make an umbilicus larger externally and it does not fall inwards, or over- 
hang, to contract it. 
The suture-line, of which the proportions are given above in relation 
first to the actual breadth of whorl in a plane and secondly to the curve 
of the whorl, shows a rather long EL with a well-marked accessory branch, 
a tridactyloid LI, and a somewhat plain L2 which does not quite reach 
down to the level of the inner dactylus of LI. 
Macrocephalites pila Nikitin, 1885 (p. 50, Pl. (VIII) X, 45, 46) from 
“lower Kelloway Clays of Elatrna,” Russia, is a similar species: primary 
ribs, however, are straight or very little curved — the figure is not clear, 
the description says nothing about curving — and proportions F. 34, -, 77, 
60, 49, 77, 18, show a much stouter shell with smaller umbilicus. The 
suture-line is somewhat similar, but the two-pointed end of LI shown by 
Nikitin looks doubtful: L2 is rather longer than in the Canadian shell and 
aux.l is larger. 
Several other species may be compared with P. jucundus: Stephano - 
ceras grantanum (Oppel) Waagen (PL XXXVI, f, 6), from the macrocephalus 
zone, has much the same proportions, but the ribs^are more laminate and 
have considerable irregularity. Stephanoceras diadematum Waagen, Pl. 
XXX, f. 3 (not PL XXX, f. 4, which is another, a much thicker species), 
also from macrocephalus zone, has ribs which are similar in their relief and 
a suture-line which is not unlike that of the present species; but it is too 
stout to be the same species; it suggests a biologically earlier form of the 
same genus, but against this is the curvature of ribs on venter and the 
greater length of L2 of suture-line. Stephanoceras subtumidum Waagen, 
from the Knutkote Sandstone (Argovian?), Macrocephalites macrocephalus 
Blake (PL III, f. 4, and Pl. III, h 5), Cornbrash ( macrocephalus zone), are 
all to be rejected on account of their very straight lateral ribbing, like as 
they are in proportions. Macrocephalites herveyi Blake (Pl. III, fig. 7, 
PL IV, fig. 1), macrocephalus zone, has somewhat the required proportions 
and also somewhat of the curved ribbing required; but differs decidedly 
in suture-line: this is not given by Blake, but I have the specimen before 
me. 
Other comparable species in the run of ribbing are Stephanoceras 
zirkeli Steinmann (p. 269, PL XII, fig. 5) and Stephanoceras chroolithicum 
Steinm. (p. 270, PL XI, 3) from Caracoles, Bolivia; but in both cases 
thickness is too great and umbilication too small. Comparison of such 
forms without any suture-line is of little value; though the likeness may 
suggest that they lived about contemporaneously. 
