378 INFERIOR OOLITE AMMONITES. 



open, coarsely ornamented. Whorl-section elliptical. Suture-line simple, with 

 short, wide-stemmed lobes ; the superior lateral lobe slightly asymmetrical ; the 

 terminal lobule slightly intra-axial, inequicellate. 



Several unusual features are found in this shell. In the costate stage most of 

 the ribs are bifurcate ; x the junction is certainly sometimes obscure, but the ribs 

 on the outer lateral area are nearly twice as numerous as those on the inner 

 lateral area, so that the outer lateral area appears regularly crenate. Further, 

 many of the ribs, instead of being direct, are slightly reflexed as well as reclinate, 

 as if to accommodate the insertion of these accessory and slightly smaller ribs. 

 Lastly, there is a very marked simplicity of the suture-line. 



None of the foregoing groups seem to accommodate this species ; it appears, in 

 fact, to be altogether isolated. Its ornamentation suggests S. subsjpinosa slightly, 

 but this association is negatived by the simple suture-line. There is also a little 

 resemblance to Sonn. decorata ; but the present form is far more coarsely 

 ornamented, with a much more elaborate spinous stage. From any of the forms 

 with which its suture-line suggests connection — forms of the submarginata-, 

 costata-, or omphalica-stocks — the peculiarities of the ornamentation, such as 

 bifurcate, irregular, reflexed, reclinate ribs, indicate a wide distinction. 



In general appearance this shell has a likeness to some species of Hammatoceras ; 

 but it has not the suture-line of that genus. 2 There is a very slight suggestion of 

 Ludivigia in the reflexed ribbing, and in the simplicity of the suture-line ; but the 

 reflexed ribbing is not sufficiently pronounced, while the spinous centre and the 

 hollow carina show that the association cannot be entertained. • 



The specimen figured is unique ; it came from Bradford Abbas, presumably 

 from the Goncavum-zone. Side and front views are shown in figs. 4, 5, of 

 PI. LXXXV ; and the suture-line in fig. 6. 



1 Bi- and tri-furcation of the spine-bearing rib in the spinous stage is not uncommon, but here 

 furcation is seen when the spines have become obsolete. 



2 See " Descent of Sonninia, &c," ' Quart. Journ. Geol. Soc.,' vol. xlv, p. 652. 



