SONNINIA SUBSPINOSA. 359 
stage with regular spines, in the neanic and ephebic stages with coste and irregu- 
larly-placed spinicostee—the latter usually parted by two to four coste; a single 
rib leads to the spine and bi- or trifurcates beyond: with age the spines decline 
to knobs. Ventral area arched, divided by a small but well-defined hollow carina. 
Inner margin ill-defined, steep. Inclusion about one-third—the overlap up to 
the spines. Umbilicus with a spinous and rather deep centre, later on shallower, 
with ribs and spines. Whorl-section elliptical. Septa complex, the lobes long, 
and fairly ornate ; the superior lateral lobe asymmetrical. 
This species has much resemblance to the young of Sonn. crassispinata a, but 
is distinguished by less elaborate ornamentation—both spines and ribs being 
smaller and closer together, and the ribs being more numerous. Yet it can 
searcely be the descendant of Sonn. crassispinata a, because it does not show the 
consequential changes which should appertain to the offspring of the latter in 
accordance with earlier inheritance. In fact, subspinosa has the same whorl- 
shape as crassispinata a, and its ornamentation is of similar pattern though so 
different in the strength of its details. It is, therefore, more reasonable to 
conclude that the two species are cousins, and to suppose, for the subdecorata- 
stock, a separate derivation from multispinata—a dwarf series, according to the 
evidence before me, which attained to scarcely larger dimensions than the 
specimen depicted. 
I figured the inner whorls of this species for the young stages of Sonn. 
acanthodes ;' but this was before the collection of Mr. Darell Stephens furnished 
older examples, showing that the slight initial differences in the intensity of 
ornament became more pronounced with age, and should not be overlooked. 
Owing, however, to the close genealogical relationship between this species and 
acanthodes, the young of this species answered the purpose of illustrating the 
brephic ontogeny of that one, and for all practical purposes will serve the same 
end now. 
Sonn. subspinosa is a rare fossil from the Concavum-zone of Bradford Abbas, 
Dorset.” It has a somewhat deceitful resemblance to certain species of 
Hammatoceras, found at about the same horizon; but its septa show that it does 
not belong to that genus, and that it is a Sonninia. 
The side and front views of Sonn. subspinosa are shown in Pl. LXXXIV, 
figs. 4,5; the suture-line, fig. 6. In Pl. XLIX, figs. 8, 9 give various details 
concerning the brephic stage of this species. It will be noticed that the whorl- 
section is, at first, depressed pentagonal, with a tendency to flatten the ventral 
1 ‘Quart. Journ. Geol. Soc.,’ vol. xlv, pl. xxii, figs. 22, 23. 
2 As Dorset and Somerset are not shires of a county town, like Gloucester-shire, Oxford-shire, 
Wilt-shire (Wilton-shire), but are the lands of the Dornseatas and Sommerseatas, the word “shire” 
should not be added to them any more tban it should to Cornwall, Kent, Essex, Northumberland, &c. 
