predecessor, as is the case in Nautilus,
the constant angle is in the neighbourhood of 80ô¯; and hence also that, in all the ordinary Ammonitoid shells, and in all the typically spiral shells of the Gastropods20, the constant angle is also a large one, being very seldom less than 80ô¯, and usually between 80ô¯ and 85ô¯. In the next place, we see that with smaller angles the apparent form of the spiral is greatly altered, and the