SONNINIA PL1CATA. 415 



Sonninia subcostata, S. Buchnan. Plate CIII, fig. 6. 

 See Plate LXXI, figs. 4, 5, and page 330. 



Add to description : — Suture-line with asymmetrical superior lateral lobe, the 

 terminal lobule intra-axial, anisosceloid ; the lateral lobules nearly isometric, non- 

 partite, not opposite. 



The removal of this species from the submargi?iata-stock (p. 328) is 

 necessary on account of the details of its suture-line. This agrees most nearly 

 with that of Sown, mutans, but in external characters the two species are so 

 dissimilar that direct genetic connection between them is unlikely. 



/3. Lateral lobules short. 



Fig. 44. — Outline of L of Sonn. plicata. 



Sonninia plicata, 8. Buckman. Plate XCVII, figs. 6 — 8. 



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

 sized, direct, reclining bullicostae and costas, inclined but obscure ventrally. (A 

 regular spinous stage lasts to about 14 mm. shell-radius, then spinicostae and 

 some costee to about 22 mm. ; x then costse and subspinicostse, first as 3 to 1, later 

 as 2 to 1 — the rib following the bullicosta generally more prominent than the 

 other in both cases, — later irregular, to about 60 mm. ; then alternate large and 

 small costse ; later costae more of a size, but somewhat unequally distant.) 

 Ventral area rounded, divided by a small hollow carina ; the core with small 

 rudimentary sulci. Inner margin fairly defined in the costate stage, and steeply 

 sloped. Inclusion about two-fifths. Umbilicus open, the central whorls 

 ornamented with the somewhat closely-set spines of the regular-spined period, the 

 outer whorls with the ribs and sub-spines passing to bulke of the irregular- 



1 These stages are obscurely shown on the other side of the figured specimen. 



