H aving 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. I was at once attracted by a specimen of Asaphus, from the Black Trenton Limestone (Lower Silurian), which has been much eroded on its upper surface, leaving the hypostoma, and what appear to be the appendages belonging to the first, second, and third somites, exposed to view, united along the median line by a longitudinal ridge. The pseudo-appendages, however, have no evidence of any articulations. But what appears to me to be of the highest importance, as a piece of additional information afforded by the Museum specimen, is the discovery of what I believe to be the jointed palpus of one of the maxillæ (Fig. 1), which has left its impression upon the side of the hypostoma—just, in fact, in that position which it must have occupied in life, judging by other Crustaceans which are furnished with an hypostoma, as Apus , Scrolls , &e. The palpus is 9 lines in length; the basal joint measures 3 lines, and is 2 lines broad, and somewhat triangular in form. There appear to be about seven articulations in the palpus itself, above the basal joint, marked by swellings upon its tubular stem, which is 1 line in diameter. There can be no reason to doubt that the Trilobita possessed antennules, antennæ, mandibles, maxillæ