i6 5 



b. Ba/anus tiiitiuuabuluui , var. costatus nov. var. PI. XIV, fig. 5 and 6. 



This form is represented by a fine specimen with very prominent ribs, the basal extre- 

 mities of which extend bevond the elongated, rounded circumference of the basis. I do not 

 know, of course, whether its shape would undergo changes during growth, and if so, what changes 

 they would be — for the present I think it best to describe it as a distinct variety. 



The shell has a very regular shape, flatly conical, with a large rhombiform orifice and 

 triangular radii, the upper margin of which runs nearly parallel to the basis. The surface is 

 distinctly ribbed, much stronger ribs alternating with groups of smaller and narrower ones. 

 The radii are feebly striated in horizontal direction, the striae representing the very delicate 

 canals which traverse them. The parietes as well as the basis have distinct pores. The outer 

 surface of the ribs is white, the furrows between them being coloured pink or red, with here 

 and there small spots coloured darker red. The greatest diameter of the basis is nearly 14 mm., 

 the shortest not quite 10 mm. 



The scutum (PI. XIV, fig. 6b ancl c) has the broad and reflexed articular ridge like the 

 other forms of this species, and the ter gum looks very much like that of a typical B. tin- 

 tiunabuluiu, its furrow being open, however, as is usual in young specimens. The spur is 

 broad and flat, and cannot be said to be distinctly produced at the internal surface of the 

 valve (PI. XIV, fig. 6a and d): differences which, probably, will change when the animal 

 grows older. 



c. B. tintinnabnlum, var. plicatus nov. var. PI. XIV, fig. 7. 



Two specimens ot this new variety were collected along with the foregoing. They are, 

 probably, young specimens. The smaller is attached to the larger and, perhaps, slightly 

 older one. 



The shape is conical, but the circumference of the basis is smaller, that of the orifice 

 relatively larger, the whole shell, in consequence, more steep than the case is with the var. 

 costatus. Corresponding ribs are present, but the stronger ones are by no means so promi- 

 nent; their basal extremities hardly extend beyond the circumference of the basis. So this 

 circumference is nearly circular, the extremities of the ribs forming small round festoons only 

 round that circumference. The surface of the ribs, of the deeper furrows, and of the spots here 

 and there along the margins of the valves, are coloured in the same way, though perhaps not 

 quite so distinctly, as in the variety costatus. The size of the basis is about 10 mm. in diameter. 



The shape of the opercular valves generally corresponds to that of the var. costatus. 

 Both forms have the lines of growth on the scutum more prominent, than, according to 

 Darwin's description, one might expect them; these lines of growth are slightly sinuous; 

 their crests — especially those near the basal margin ■ — are furnished moreover with a row 

 of minute points, and consequently are slightly crenated. The tergum has the furrow open and 

 relatively broad ; the spur as a whole is, however, not quite so broad as in the variety 

 costatus, its extremity is slightly more rounded. The crests for the tergal depressor muscle 

 are, in this variety, not quite so strong as in the var. costatus. 



37 



