Some New Silurian Trilobites

Abstract

Pygidium elongated, sublanceolate, bluntly pointed posteriorly. Lateral lobes flattened, horizontal, composed of three pairs of pleurae and a median postaxial piece. Axis short, conical, convex, tapering rather rapidly to blunt tip, less than one-third the length of the pygidium and about one-third its width, subcarinate posteriorly, faintly marked off from postaxial piece by weak circumscribing furrow; furnished at anterior end with one strong narrow complete ring, marked off by strong furrow, followed by weaker second ring defined by faint complete furrow, and with traces of a third incomplete ring; posterior two-thirds of axis devoid of annulations. Postaxial piece long, narrow, widening somewhat posteriorly, descending gradually to level of lateral lobes from tip of axis and becoming flattened but distinctly carinated for its whole length. First lateral pleura strongly falcate, bending back suddenly at fulcrum where it is widest and thence narrowing rather slowly to acutely pointed free tip projecting backwards beyond margin; pleural furrow submedian, diagonal, parallel to posterior edge of pleura, running nearly to tip. Second lateral pleura elongate, sublanceolate with tip bent back slightly and projecting freely beyond margin as short recurved point; pleural furrow median, slightly diagonal, not reaching tip. Third lateral pleura sublanceolate, broader than second pleura, incompletely marked off from postaxial piece posteriorly, the bounding furrow not quite reaching the margin but curving gently outwards at its end; tip of pleura undefined and not projecting beyond margin; pleural furrow median, slightly wavy, running nearly straight back parallel to its fellow, curving inwards a little at its end but not clearly connected with bounding furrow. All pleural and interpleural furrows of equal strength. Posterior lateral margins of pygidium behind tips of second pleurae forming nearly half its length and describing a long simple slight curve on each side, uniting behind in a blunt point at about 60°, the median carina of the postaxial piece extending to its tip.