DESCRIPTION OF PLATES, 15, 16. 649 



side of the shell, formed by the folded walls : the blacker 

 part is the epidermis ; the lighter part is the yellowish 

 fibrous tissue of the skin under the epidermis. 

 Fig. 5, Coronula reginse, shell seen from the outside. 



6, Coronula barbara, internal view of the basal margin and inside 

 of one of the compartments, exhibiting the circumferential 

 transversely looped ends of the folds of the wall, with the 

 inner surface transversely wrinkled. 



7 — 9, diagrams, showing how one of the circumferential trans- 

 verse loops of the wall becomes divided into two transverse 

 loops, thus giving rise to another fold in the wall. 

 10, diagrams, showing how the wall of the young shell in Coro- 

 nula, from being (a) simply sinuous, becomes deeply 

 folded (b) ; the folds lastly (c) expanding transversely at 

 their ends, thus giving rise to the circumferential trans- 

 verse loops, as in fig. 7. 



PLATE 16. 



Genus — Coronula. 



Fig. 1, rostrum, viewed from the inner side, of Coronula diadema. 



a, sheath, marked transversely in the upper part by the attach- 

 ment of the opercular membrane. 



by furrow on each side of («), receiving the edges of the thick 

 alee of the adjoining lateral compartments. 



c", special plate, on which the alee on their outer sides rest. 



d, radius, on the edge it may be just seen to consist of an outer 



layer (the normal radius), and a much thicker inner part 

 (the pseudo or complementary radius) formed of oblique 

 denticulated septa. 



e e' e", basal edge of wall, which from its commencement at 

 e, or e" can be followed, folding up to near the basal edge 

 of the sheath, to its termination at e" or e. 



y, serrated lines of junction between the folds of the wall. 

 2, Lateral compartment of C. diadema, seen laterally, on a smaller 

 scale than last fig., but taken from the same shell ; 

 letters of reference the same : this figure, if the ala a' were 

 removed, would do for a lateral view of the rostrum, or 

 fig. 1. 



a, sheath, much foreshortened; 



a', ala (therefore also part of sheath), and the edge of which 

 fits into b of fig. 1. 



by furrow receiving edge of ala of the adjoining carino-lateral 

 compartment. 



c", special plate, seen edgeways. 



d s radius, the division into two parts, viz., the thin outer nor- 

 mal radius, and the under pseudo or complementary radius 

 here shown (rather exaggerated) plainer than in fig. 1. 



e, basal edge of wall ; to the right hand the three folds at their 



inner ends are seen obliquely, one behind the other: 

 these are seen directly in front in fig. 1. 



