[194] Journ. of Conch. vi. p. 123.
[195] Phil. Trans. 1889, vol. 180 B, p. 207. A somewhat similar case (the celebrated Steinheim series of Planorbis) is dealt with by Hilgendorf, MB. Akad. Berl. 1866, p. 474; and Hyatt, Proc. Amer. Ass. Sc. xxix. p. 527.
[196] J. B. Bridgman, Quart. Journ. Conch. i. p. 70.
[197] W. C. Hey, Journ. of Conch. iii. p. 268.
[198] Zool. Anz. xiii. p. 662.
[199] J. Madison, Journ. of Conch. v. p. 260.
[200] Quart. Journ. Conch. i. 339.
[201] Whitfield, Bull. Amer. Mus. N. H. i. p. 29.
[202] Amer. Nat. xiv. p. 51.
[203] Animal Life, Ed. 1, p. 160 f.