See, however, Goodrich, Quart. Journ. Micr. Sci. xlv. 1901, p. 311.
Bashford Dean, Anat. Anz. xi. 1896, p. 673.
Budgett, Trans. Zool. Soc. xvi. Part vii. 1902, p. 328.
Thacker, Trans. Connecticut Acad. iv. 1877, p. 233.
Traquair, Geol. Mag. vii. 1890, p. 15; Goodrich, l.c.