402 INFERIOR OOLITE AMMONITES. 



Sonninia nuda, S. Buchnan. Plate CIII, fig. 10. 



See Plate LXXXII, figs. 3, 4, and page 352. 



Add to description : — Suture-line of the type with long lobes, L with a long, 

 slightly intra-axial, isosceloid terminal lobule, and an outer lobule bipartite to its 

 base, making the outer lobule duplicate. 



The suture-line of this form agrees with that of Sonn. crassiformis in having 

 the outer lateral lobule of L cleft to the base, and in other features. As the 

 outer lateral lobule of L in Sonn. crassa is only half-cleft, that species can 

 scarcely be placed in direct genetic connection between crassiformis and nuda; 

 because it is presumed that a lateral lobule of L bipartite to the base is a further 

 development than a lateral lobule only partially bipartite. 



The foregoing forms, from crassicostata (p. 398) to this species, excluding 

 insequa, were included as the crassa-stock (p. 347). The above study of their sep- 

 tation confirms their close relationship, but it shows that in the crassa-stock there 

 were more than two branches. 



2. Lobes somewhat short, not very ornate. 



Sonninia duplicata, 8. Buchman. Plate XCIX, figs. 1 — 3. 



Discoidal, compressed, hollow-carinate. Whorls ornamented with long, 

 slender, regular spines to about 40 mm. diameter ; with plain costae and irregular 

 spinicostse, as 2 or 3 to 1, to about 85 mm. diameter; with subarcuate, reclining, 

 ventrally-inclined, irregular-sized costse, and occasional bullicostae to 120 mm. 

 diameter; lastly, with similar costas roughly arranged in pairs, the pairs larger 

 than their fellows, and obscurely connate on the inner third. Ventral area 

 arched, divided by a small, fairly distinct hollow carina. Inner margin fairly 

 marked after the irregular spinous stage, slightly subconvex. Inclusion one- 

 third — not up to the spines of the irregular spinous stage. Umbilicus with 

 gibbous whorls and long slender spines. Whorl-section subquadrate-oval. 

 Suture-line with a tetradactyloid L, the outer lobule being bipartite, the terminal 

 lobule slightly intra-axial but isosceloid and equicellate. 



The somewhat irregular pairing of the ribbing distinguishes this species. 

 This character is similar to what obtains in Sonn. hiplicata (p. 345) and Sonn. 

 alternata (p. 346). From the first the present species is distinguished by its septa- 

 tion — L being shorter, less ornate, and more symmetrical, — by the less reclinate 



