362 INFERIOR OOLITE AMMONITES. 
The suture-line is the only matter for doubt; for the superior lateral lobe is 
scarcely so branched, and is rather wider-stemmed than would be expected. 
Perhaps degeneration of the septa, which is often a phylocatabatic feature, may 
account for this. Such a surmise seems supported by the suture-line at an earlier 
age, when, as seen through the crystalline test, it is narrower-lobed and pro- 
portionately more ornate. 
Of this interesting little species there is in my cabinet only one specimen, 
obtained from the collection formed by Mr. Darell Stephens, F.G.S., &c. It is 
from the Concavum-zone of Bradford Abbas. Side and front views, and suture- 
line are illustrated in Pl. LXXXIV, figs. 12—14. 
The omphalica-stock. 
In this stock are two forms distinguished by the large size of the umbilicus in 
correlation with somewhat compressed whorls, considerable decline in ornamenta- 
tion, and a degraded type of suture-line. They belong to the costate stage of 
phylocatabatic development, and illustrate two gradations of decline. From each 
other they may be separated thus: 
S. ewromphalica, centrally spinous, costate. 
S. omphalica, rudimentary spines, costate. 
The simple septa, with asymmetrical superior lateral lobes, of Sonn. ewrom- 
phalica suggest connection with the submarginata-stock; the more degraded 
septa of Sonn. omphalica, with their almost aborted lateral lobules, have resem- 
blance to the septation of Sonn. costata. The general proportions—considerable 
compression correlated with wide umbilication—are similar to what obtains in 
both the submarginata- and costata-stocks ; but the spinosity correlated herewith 
is too much for descent from 8S. costata, and too little for descent from S. sub- 
marginata ; regard, of course, being paid to the amount of compression and the 
width of umbilicus with which a given degree of spinosity is associated in these 
cases. 
Sonninta EUROMPHALICA,' S. Buckman. Plate LXXXV, figs. 1—3. 
Discoidal, compressed, hollow-carinate. Whorls ornamented, at first, with 
fair-sized regular spines, which presently are irregular, and then die away—only 
1 Edpus, broad ; dupadds, umbilicus. 
