METOICOCERATID 4. 123 
have the umbilicus smaller and the inner row of the two outer lines 
of tubercles elongated longitudinally and parallel with the outer rows. 
The sutures are more complex at an earlier stage and remain more 
complex throughout life as regards their marginal digitations. The 
first lateral lobes are also narrower and longer in proportion in the 
later stages than in swallovi, and the inflections are more numerous 
at the same age, being from six to seven, instead of five or six as 
in swallovi. The youngest stage seen (Pl. XIV, figs. 1,2) had a living 
chamber complete near the umbilicus and not quite three-fourths of a 
volution in length. Several specimens showed a completed living 
chamber near the umbilical shoulders and on the sides, and in adults it is 
much shorter, invariably one-half of a volution in length. The sides 
were smooth and flat at the beginning of the outer volution in this specimen. 
The costee appeared as shown in the figure and nodal termini were devel- 
oped on the last costation near the aperture. These were also present in 
the specimen shown in fig. 4, but, as may be seen in figs. 2 and 5, these were 
not prominent as in swallovi. The same is true of all of the seventeen 
specimens examined besides Pl. XIII, fig. 4 The elongated second row of 
lateral tubercles found in fig. 4 is also perceptible to some slight extent in 
the specimen fig. 7, but is absent in younger stages and is not present at 
any stage in some specimens. This second row of tubercles may be very 
slightly developed in some specimens, and the cost are also much less 
pronounced and the venters narrower than in those figured. ‘The other two 
specimens show a much stouter form with broader venters and more promi- 
nent cost. These can only be separated from true swallovi by their cost, 
flatter sides, and less prominent umbilical nodes. 
An old suture of this species is shown on Pl. XIII, fig. 5. This was 
the basal suture of a fragment of the living chamber of a fossil of about 
the same size, probably, and age as the one shown on Pia hoa 
The differences of this suture appear to be considerable when com- 
pared with Pl. XIV, fig. 8. The external characters of this fossil are 
equally decided, but the absence of the internal volutions and the 
variability of the sutures in this species does not justify the 
separation of this as distinct from white. The latter part of 
this living chamber and the whole of another larger fragment has 
huge fold-like coste that cross the venter, cutting it into waves. The 
costee are flat on the venter with abrupt forward edges. The ventro-lateral 
