In the Geological Magazine for July, 1871, Plate VIII. pp. 289–294, I published an article on the above subject, giving my views of the appendages of Trilobites, and reproducing the figure of Asaphus platycephalus, Stokes, showing traces of eight pairs of locomotory appendages, discovered by Mr. Billings in the Trenton Limestone, city of Ottawa, and described and figured by him (in Quart. Journ. Geol. Soc. 1870, pp. 479–486, and plates xxxi. and xxxii.). I also appended a note to Mr. Billings's paper (op. cit. 1870, pp. 486–488) on a palpus of Asaphus from the same locality, which is as follows:—“Having been requested by Sir William Logan to examine the Trilobite sent over by Mr. Billings from Montreal, I was led to compare it with certain specimens in the British Museum collection, presented by Dr. J. J. Bigsby, F.R.S., some years since.