SONNINIA NODATA. 369 
attainment of the compressed, involute form than Sonn. spinosa, has yet gone 
further in the matter of loss of spines; and these differences are maintained in 
the development of the descendants of these two species. 
Internally, in the matter of suture-line, there is a particular distinction 
between the members of the paucinodata- and quadrifida-stocks. In the former 
the superior lateral lobe has a decided want of symmetry, on account of the cell 
parting the outer and terminal lobules being considerably deeper than the cell 
parting the terminal and inner lobules; and consequently, the lateral lobules are 
not opposite,—that is, the inner lobule, in this case, leaves the main stem further 
back than does the outer lobule. Technically, then, the superior lateral lobe in 
this series is asymmetrical on account of the terminal lobule being intra-axial,’ 
distinctly anisosceloid, and inequicellate. In the quadrifida-stock the superior 
lateral lobe is symmetrical, the terminal lobule axial, isosceloid, and equicellate 
(see page 364). 
SonnintA Nopata, S. Buckman. Plate LXXXIX, figs. 1—3; and allied young 
form, Plate LX XXIX, figs. 4, 5. 
Discoidal, compressed, hollow-carinate. Whorls ornamented with rather 
small, not prominent, subarcuate, much reclined, ventrally-inclined coste, of which 
about every second or third carries a small median knob—the knob-bearing costz 
more prominent than their fellows. (The regular spinous stage lasts to a diameter 
of about 25 mm., then follows an irregular spinous stage—spinicoste to coste 
about as one to three—to about 70 mm. diameter; to this succeeds the stage 
when every second or third costa is nodate; later still the nodicostz are more 
numerous.) Ventral area obtusely arched, medianly flattened, bearing a small, 
fairly-defined, sub-impressed hollow carina. Inner margin practically undefined. 
Inclusion about one-third, not up to the spines. Umbilicus concentric, with 
gibbous-sided whorls. Whorl-section oval. Suture-line with an asymmetrical 
superior lateral lobe; the terminal lobule intra-axial, distinctly anisosceloid and 
inequicellate ; the lateral lobules not opposite. 
Compared with Sonn. spinosa this species is less elaborately spined, more 
roundly whorled, and more umbilicate. It cannot be derived, therefore, from 
Sonn. spinosa ; because, while the degree of spinosity is more retrograde, the 
other features are less so than in that species. For opposite reasons spinosa 
cannot be derived from this species: further, any such idea of derivation is at 
1 Intra-axial, inside the line of the main axis ; if outside it would be ultra-axial. 
47 
