[32]

Var. (a) (figs 5c, 5d). With respect to this remarkable variety, anyone would at first think it specifically distinct. The shell is much compressed, or elongated in the rostro-carinal axis, sometimes to a great degree; I have seen a specimen 0*25 of an inch in this axis, and only o*i in its broadest part; but this is a very unusual degree of elongation. The most remarkable character is the extraordinary narrowness of the carina, o f the carino-lateral compartments, and of the rostrum, compared with the great breadth, especially along the basal margin (fig. 5d), of the lateral compartments. The radii are of unusual breadth. The tips of the rostrum and of the lateral