SONNINIA LOCULOSA. 437 



septal unlikeness. It will, however, be seen that, besides many differences in 

 detail, the lobes of dominans are about twice the length of those of domina.tr ix. 

 Such an inequality of dimensions must point to considerable differences in the 

 anatomical details of the soft parts of the animals in these two species. 



It may be noticed that the suture-line of this species 1 has considerable 

 resemblance to that of Sonn. biplicata (PI. LXXVIII, fig. 3), which has the outer 

 lobule strongly bipartite. In this species, however, the lobes are rather longer in 

 proportion to the whorl, they are thinner-stemmed and more ornate. Further, 

 the terminal lobule is anisosceloicl and less intra-axial. These features do not seem 

 to allow this species to be placed as the descendant of biplicata. 



Young Sonn. renovata is not unlike this species, but it is decidedly more 

 umbilicate, has more gibbous-sided whorls, and a different septation. Adult 

 renovata is entirely different, because of its large bullicostEe. 



Though it agrees in the length of its lobes with Sonn. locuples /3, yet the 

 immature Sonn. dominans shows differences of detail ; for instance, the terminal 

 lobule of L is isosceloid, and the stem of the lobe is wider. The bipartition of the 

 outer lobule of L is similar, though very much deeper. 



Sonninia loculosa, S. Buchnan. Plate XCII, figs. 5 — 7. 



Discoidal, compressed, hollow-cainnate. Whorls ornamented with closely-set, 

 ill-defined, not prominent, direct, slightly-reclining costas (details of the central 

 whorls wanting). Ventral area rounded, divided by a small hollow carina. Inner 

 margin well-defined, broad, nearly flat, nearly upright. Inclusion about two-fifths. 

 Umbilicus small, slightly excentric. Whorl-section oblong, very slightly gibbous 

 laterally. Suture-line with long ornate lobes, the side being almost completely 

 occupied ; the siphonal lobe with deeply divided terminal lobule and three 

 accessory lateral lobules, of which the middle is large and important, the other 

 two somewhat aborted ; L tetradactyloid on account of duplication of the outer 

 lobule ; the terminal lobule very intra-axial, isosceloid, long, being longer than the 

 main stem, and it penetrates the stem of the preceding lobe to touch the part 

 which connects the terminal lobule with the inner branch of the outer lobule ; the 

 inner lobule about equal in size to one branch of the outer lobule. 



This species is very like modesta (PI. XCV, figs. 3 — 5), and is in fact its 

 morphic equivalent ; the only external difference is a slightly greater thickness, 

 most perceptible near the inner margin, owing to a slight gibbosity of the side of 



1 The immature form is considered. 



