650 DESCRIPTION OF PLATE, 16. 



Fig. 3, lateral compartment of C. balcenaris, seen laterally ; letters of 

 reference the same as in last fig., but c" not introduced for 

 this plate is barely developed, and only in the lower part, 

 and is attached to the radius : g g points where fresh folds 

 have been formed in the walls along the lines of suture, 

 as may be seen in the outline of the wall in fig. 5. 



4, lateral compartment of C. regince, seen laterally ; letters of 



reference the same as in the last two figures. 



5, Coronula balaenaris, outline of the basal margin of the folded 



walls: s y s, the six sutures. The wall can be continu- 

 ously followed from one end of a suture to the next 

 suture. 



6, Coronula diadema; small portion of the external surface of the 



wall, close to the basal edge, highly magnified ; a, outer 

 lamina, not extending down to the basal edge ; b, inner 

 lamina ; c, projecting longitudinal septa. 



7, Coronula diadema ; transverse section through the upper part 



of the shell, showing the rostrum and the two adjoining 

 lateral compartments (and the alze of the carino-lateral 

 compartments), all supposed to be a little separated from 

 each other, so that the sutures, s s, are shown by white 

 lines. 



a a a, rostrum. 



c e, lateral compartments. 



d D, carino-lateral compartments, of which only the alae (a') 

 are shown. 



Of the letters in italics, those which occur in figs. 1, 2, 3, 

 4, 5, refer all to the same parts, viz. : — 



a, sheath, continuous with («') the alae, where such occur. 



c", special plate on which the alse rest. 



d, radius, divided into a thin outer normal radius, and the inner 



complementary portion, the latter shaded by convex lines 

 of growth. 

 d' is a special tube (seen only as a black dot) for a thread of 

 corium. 



e, folded walls. 



/, junction of the folded walls (see/, in fig. 1) leading into 

 the cavities (/') open beneath, and filled up by the epider- 

 dermis (see PL 15, fig. 4) of the whale. 



h, inside of the transverse loops of wall, occupied by corium : 

 in the enlarged section of a loop, in C. balsenaris, in PL 15, 

 fig. 2 a, the opposed sides are seen to be connected by 

 shelly longitudinal plates. 



v, cavity occupied by the ovarian tubes and CEeca. 



