368 INFERIOR OOLITE AMMONITES. 
divided by a small ill-defined (hollow ?') carina. Inner margin well defined, 
nearly upright (later, falling off a little more), subconvex. Inclusion about three- 
tenths. Umbilicus decidedly excentric (beginning at about 27 mm. umbilical 
diameter, about 90 mm, diameter of the shell), at first small and somewhat 
deep. Whorl-section oblong (slightly ventrally convergent). Suture-line with a 
symmetrical, cruciform superior lateral lobe, of which both the outer and the 
inner lobules are nearly equipoised and distinctly bipartite ; the terminal lobule 
long and tapering, axial, equicellate, and isosceloid. 
The long, taper terminal lobules and the bipartite, equipoised, laterally-pro- 
jected lateral lobules have a certain resemblance to the shape of the abdomen 
and wings of various Lepidoptera. Hence this type of superior lateral lobe may 
be called “ papilioniform,” and the species ‘‘ papilionacea.”’ 
The only species at all lke this one are Sonn. substriata and Sonn. parvicostata ; 
but both of them differ entirely in their septation. Further, this species is more 
costate than either of them. 
The agreement in suture-line, costation, and general appearance warrants my 
placing this species as the descendant of Sonn. quadrifida. It differs only in the 
features which the development of that species would possess,—that is to say, it is 
less spinous, less costate, and less umbilicate—the excentricity of the umbilicus 
being apparent atan earlier age. In comparing this species with Sonn. quadrifida 
in regard to earlier inheritance it may also be noted that larger coste—larger, 
that is, than their predecessors—make their appearance in this species at a rather 
earlier age than in that one. 
Sonn. papilionacea occurs in the Concavum-zone of Bradford Abbas. The. 
side view of the type-specimen, reduced to one-half natural size, is shown in fig. 1 
of Pl. XC; the outline of the whorl-section, similarly reduced, in fig. 2; the 
septain fig.3. The lettering of this figure suggests the correlation of homologous 
parts in this and two other superior lateral lobes of very different types ; further, 
this lobe may advantageously be compared with another type of superior lateral 
lobe belonging to an outwardly homceomorphous fossil, namely, fig. 6 (Pl. XC). 
The paucinodata-stock. 
Externally the various species of this stock may be at once separated from 
their respective morphological equivalents in the quadrifida-stock by being, 
relatively to retrogression in other characters, less spinous. Thus Sonninia 
nodata, which in its general characters has made far less departure towards the 
1 The core is practically uncarinate until the body-chamber is reached. 
