SONNINIA DIVERSA. 355 
The side view of an immature shell is shown in Pl. LXXX, fig. 4, and the 
section of its whorl] in fig. 5. The suture-line from a larger specimen, biologi- 
cally somewhat nearer to crassibullata, is given in fig. 6. 
Sonninta Diversa, S. Buckman. Plate LXXXIII, figs. 1—4; an allied form, 
Plate LX XX], figs. 5, 6. 
Discoidal, compressed, hollow-carinate. Whorls, in section, circular to 
oblong, ornamented, first, with tall, slender, closely-packed, regular spines ; 
afterwards by direct, nearly upright, somewhat irregularly-placed cost, obscure 
on the outer area. Ventral area rounded, divided by a fairly-defined hollow 
carina. Inner margin well-defined, nearly upright, flat. Inclusion one-half. 
Umbilicus ornamented with numerous tall spines. 
This species is biologically later than Sonn. crassicostata, and practically 
speaking it may be regarded as its descendant, though strictly it comes from a 
form intermediate between crassibullata and crassicostata. The regularity of its 
numerous, closely-packed spines in the inner whorls gives it a very distinctive 
appearance, besides separating it from crassinuda, in which the spines soon become 
irregular. 
What appears to be a further development of this form is shown in figs. 5 
and 6 of Pl. LXXXI. It will be noticed that it has the same well-marked 
regular spines, but they end at a much earlier age. It is lke crassinuda, 
but does not show an irregular spinous stage. It is as widely umbilicate as 
crassinuda a, but much thinner; it is as thin as crassinuda B, but more 
umbilicate—it is also less spinous, and becomes smooth sooner. Therefore, 
compared with crassinuda, it is more umbilicate in proportion to thickness, or 
thinner in proportion to the size of its umbilicus. These facts seem to indicate 
its separation from crassinuda, and that in position it is the connecting link 
between diversa and levigata. The regular spines of the central whorls, lasting 
longer than the regular spines in crassinuda, link it to diversa by the law of 
earlier inheritance; the smoothness of its outer whorl and its thin, umbilicate form 
link it to levigata by the same law. 
Sonn. diversa is distinguished from crassicostata by the greater number of 
smaller spines; from dominans and its allies by the absence of an irregular 
spinous stage, and by the sudden decline from well-marked spines to poorly- 
marked cost; from crassinuda by the remarkable regularity of its spines. 
