Figure 7. Thin section from yellow limestone. Grzybowskia jasoni. The size of the protoconch is 105 ±5 µm, which is smaller than the modal size, possibly because this section is not through the center of the test, particularly on the side in contact with the deuteroconch. (Most "A" generation protoconch chambers are in the range of 150 µm to 200 µm.) In this specimen, there is one post embryonic whorls before the adult stage begins with the acquisition of secondary chamberlets. Just before reaching two whorls, at the point marked "A," the rate of whorl expansion appears to increase, but passes out of the plane of this section. At this point, the secondary chamberlets become more numerous.

Thin section FFC 4B shows the maximum dimension is 1.54 mm.