SONNINIA PAPILIONACEA. 367 
if the cost are similar the spines are smaller—are those given below ; and their 
differences may be stated thus: 
Sonn. dominans, type' (Pl. LXV1I), is thicker, less spinous, more umbilicate. 
Sonn. revirescens (Pl. LXX, fig. 1) is less costate (in earlier stage), less 
umbilicate, less carinate, sharper ventrally. 
Sonn. submarginata (Pl. LXXI, figs. 1—3) is more umbilicate, less spinous— 
the spines more irregular,—and has an asymmetrical superior lateral lobe. 
Sonn. semispinata (Pl. LXXVII, figs. 1, 2) is thinner, more angular, less 
spinous, more costate—the costz obsolescent with age,—less carinate. 
Sonn. crassa (Pl. LXXXII, figs. 1, 2) is far thicker, less umbilicate, more 
coarsely ornamented. 
Sonn. diversa (Pl. LX XXIII, figs. 1, 2) is more costate, and has a larger number 
of more closely-set spines. 
The agreement in the matter of suture-line causes me to place this species as 
the descendant of spinosa, though there is, obviously, room for several inter- 
mediate species. The four points made by the bipartition of the lateral lobules 
suggest the name quadrifida. 
The reduced size at which this species has been figured, necessitated by the 
desire not to carry any of the Sonninine of the Concavum-zone into Vol. II, has 
given the shell a somewhat false appearance, and its identification is accordingly 
rather more difficult. In this connection, however, it may be noted that the 
features of the suture-line are a very sure guide: the symmetry of the superior 
lateral lobe and its bipartite lateral lobules are very noticeable. 
Sonn. quadrifida occurs in the Concavum-zone of Bradford Abbas. ‘The side 
view of the type-specimen is illustrated in fig. 1 of Pl. XCI; and in fig. 1 ais given 
a further portion of the end of the whorl (it is broken away in fig. 1), showing that 
the ribs of the core are becoming larger with age. The outline of the front view 
is given in fig. 2 (a—a): the figs. 1, la, and 2 are half natural size. Two 
consecutive septa, ultimate and penultimate, are shown in fig. 3; they are of 
natural size. 
Sonninia Papinionacna, S. Buckman. Plate XC, figs. 1—3. 
Discoidal, compressed, carinate. Whorls ornamented with direct, closely-set, 
inconspicuous, upright, ventrally-inclined coste, which tend to become rather more 
distant and a little more prominent after about 120 mm. diameter. (Spinous 
stage ends about 28 mm. diameter.) Ventral area rounded, slightly flattened, 
1 It will be explained later on why only the type dominans is mentioned. 
