Redescription of Marella Splendens (trilobitoidea) from the burgess shale, middle cambrian, British Columbia

<jats:p xml:lang="en">Previously studied specimens and additional material from old and new collections have been prepared with attention to those oriented obliquely, laterally, and vertically, as well as approximately parallel, to the bedding. New photographs accompanied by explanatory line drawings are given, as well as reconstructions of the animal in various aspects. The cephalic shield was wedge shaped, and bore two large pairs of spines; no compound eye or facial suture of trilobite type has been observed; the presence of a pair of projections on the posteroventral edge of the shield is demonstrated, these projections being part of the labrum. The first two appendages, the anterior of thirty segments, the second six-segmented with the distal five setose, are thought to represent first and second antennae and to have been attached to the body in the posterolateral region of the cephalic shield. The post-cephalic body, of twenty-four to twenty-six somites, ended in a minute telson and lacked pleurae; each somite bore a pair of biramous appendages. The basal segment was long, subcylindrical; five additional segments formed what was presumably a walking leg; a branch bearing filaments was attached to the proximal part of the basal segment. This flexible branch may have been in life swung backward and forward and rotated through an arc of some 140 degrees; it may have functioned as a gill. Moulted exoskeletons of the cephalic shield are found extremely rarely; most individuals were complete when entombed. The associated dark stain in the rock, in many places surrounding the posterior part of the body, has yielded by acid extraction nearly a full suite of protein amino acids, suggesting that soft parts had not decayed before burial. These observations support the view that the fossils are of individuals of a living population that was catastrophically buried.</jats:p>