Bumastus is a large trilobite, reaching a length of . The body is oblong-oval, about twice as long as it is wide, Like all trilobites, the body is divided into three functional segments known as
tagmata (singular: tagma), which in turn are divided into three lobes - the central lobe (axial) and two lateral lobes (pleural). Aside from faint depressions in the
thorax,
Bumastus is unusual in that the three lobes are barely discernible from each other. The axial lobe of
Bumastus is also very broad in comparison to the pleural lobes. The
genal
angles of the cephalon - the edges where the lateral and rear margins of the cephalon meet - are rounded. The cephalon is
effaced (smooth and mostly featureless), an
evolutionary trend also seen in
Illaenus and
Trimerus, though not as pronounced as that of
Bumastus. The
glabella (the central lobe of the head) is almost fused to the
fixigena. The pygidium completely lacks any visible trilobation. It is usually semicircular in shape but can be pointed in some species like
B. niagarensis. The smooth
compound eyes are large and peculiarly well-developed. This, along with the rounded contours of their body, suggests that
Bumastus may have spent most of its time buried in sediment with its eyes protruding. The surface of the exoskeleton of most species is studded with minute punctures. ==Paleoecology==