Notes on some Specimens of Lower Silurian Trilobites

Abstract

This specimen was collected in the Trenton Limestone, at the city of Ottawa, about ten years ago. When discovered it was lying flat upon a thin slab of limestone, and well preserved, with the exception of the eyes, which seem to have been forced inwards by pressure from above. It was also divided into two pieces by a fissure which extended diagonally across, from the first segment of the thorax on the left side to the fifth segment on the right. It remained in the Museum for several years without attracting particular attention, until one day, observing that the part in front of the fissure was somewhat loosely attached, I removed it, and was surprised at finding, on the underside, not only the hypostoma in place, but also what appeared to be some of the legs of the animal. As the part behind the fissure was more firmly attached to the stone, I had it cut across just behind the eighth segment by the lapidary of the Survey. The remainder of the thorax was then easily split off. The pygidium came off with difficulty and in two pieces. All the pieces were then fastened together; and we thus obtained two specimens, one of which shows the underside of the Trilobite, and the other its impression on the stone. On the underside (P1. XXXI. fig. 1) a broad shallow grooye extends from the space between the two lobes of the hypostoma, where we must suppose the mouth to be situated, backwards