SONNINIA OMPHALICA. 363 
an occasional rib being a little bullate: the greater part of the fossil ornamented 
with direct, slightly-reclining, ventrally-inclined ribs. Ventral area, with test, 
flattened, almost medianly-sulcate,—the depression divided by a small, well-defined 
hollow-carina: without test, carinate-bisulcate, the carina small, the sulci unmis- 
takable. Inner margin ill-defined, steep. Inclusion about one-third. Umbilicus 
open, graduate. Whorl-section nearly quadrate. Suture-line simple, with rather 
broad-stemmed lobes. 
This form, the morphological equivalent of Sonn. submarginata, to which it 
has much resemblance, differs in its shorter spinous stage, coarser ribbing, flatter, 
Squarer ventral area, and more quadrate whorls. It is more likely to be 
confounded with Sonn. cymatera until the eye has become expert to detect the 
difference in the reclination of the ribbing—so marked a feature of that species. 
Sonn. euromphalica is, however, also distinguished from cymatera by its smaller 
ribs more closely set—as three to two,—by its flat-sided whorls, steeper inner 
margin, and by having more of the regular and fewer of the irregular spines. 
In Pl. LXXXV, figs. 1—3 give side and front views and suture-lines of this 
species, which is from the Concavwm-zone of Bradford Abbas, Dorset. It is 
doubtful if it be an adult shell, but it is unlikely that it reached a large size. The 
specimen is almost complete—it has half a whorl of body-chamber. 
Sonninta oMPHALIOA, S. Buckman. Plate LX XXIII, figs. 5—9. 
Discoidal, compressed, carinate. Whorls ornamented, in the brephic stage, 
with small regular spines, soon yielding to spines and ribs, passing in the neanic 
stage to ribs and nodicostw, and then to plain costez ; the presumably ephebic stage 
with fairly-marked, somewhat distant, rounded, direct, slightly-reclining, ventrally- 
inclined (almost ventrally-projected) ribs. Ventral area, neanic, almost sulcate, 
divided by a well-marked, presumably hollow carina; ephebic, somewhat flattened, 
divided by a small, rounded carina,' which tends to become obsolete in the middle 
ofa more sloped area. Inner margin not defined till the plain costate stage is 
well commenced, then smooth and steep, later on more sloped. Inclusion about 
two-fifths. _Umbilicus shallow, open, graduate. Whorl-section, neanic, sub- 
circular; ephebic, elliptical. Suture-line simple, with broad-stemmed lobes; in 
the superior lateral lobe the lateral lobules are presumably aborted, the cruciform 
arrangement not being shown. 
This species is chiefly remarkable for the size of its umbilicus in proportion to 
' There is a slight tendency to form a crenulate carina on the early part of the body-chamber. 
