366 INFERIOR OOLITE AMMONITES. 
costz. In this, as in some other allied species, the bullicoste are mere thickenings 
of the test, and there are consequently no corresponding elevations of the core. 
This fact, as well as the analogy with other species, indicates preparation for a 
plain costate test—it is a sign of retrogression. 
In identifying specimens with this species it is necessary to give a word of 
warning. Apparent similarity of ornamentation, especially in the young stages, 
is misleading. The similarity of ornament must be accompanied by a suture-line, 
with an isosceloid, equicellate terminal lobule to the superior lateral lobe, which 
should itself be fairly symmetrical. The delineation of the suture-line of the type 
is not altogether satisfactory, owing to indifferent preservation of the core: this 
has given the lobes and lobules a greater breadth of stem than they would 
properly possess, and some of the minor details are obscured. 
Sonn. spinosa oceurs in the Concavwm-zone of Bradford Abbas. The type- 
specimen, a fairly well-preserved example with the greater portion of its test 
present, is illustrated in side view, fig. 7, Pl. LXXXI; the outline of its whorl- 
section in fig. 8; and its suture-line in fig. 9. 
Sonnrnta QuapriFipa, S. Buckman. Plate XCI, figs. 1—3. 
Discoidal, compressed, hollow-carinate. Whorls ornamented with direct, 
fairly-close, not prominent, almost upright,’ ventrally-inclined costa, which become 
more distant” after about 145 mm. diameter. (The regular spinous stage lasts to 
about 30 mm., the irregular spinous stage to about 45 mm. diameter.) Ventral 
area arched (in adult the median part somewhat flattened), divided by a well- 
defined, rounded hollow carina, which, with age, becomes less conspicuous, 
smaller, and more impressed. Inner margin not well-defined till the early costate 
stage, then steeply sloping, subconvex; the portion abutting against spines 
formed with niches for their reception (indented for spines). Inclusion about 
three-tenths. _Umbilicus slightly excentric—after about 130 mm. diameter. 
Whorl-section oblong. Suture-line: with a symmetrical, cruciform superior 
lateral lobe, of which the lateral lobules are equipoised and bipartite; while the 
terminal lobule is long, taper, axial, equicellate, and isosceloid. 
The nearest morphological equivalents of this species, though several of them 
show less difference in relative proportions of costate and spinous stages—that is, 
1 Rather more reclinate on the last half-whorl. 
2 On the core the costs are rather prominent, but where the test is present they are no more 
prominent than before. 
