Ellipsocephalus

Ellipsocephalus Zenker, 1833, is a genus of blind Cambrian trilobite, comprising benthic species inhabiting deep, poorly lit or aphotic habitats. "E. hoffi" is a common trilobite mainly from central Europe (Czech Republic).
Description.
"Ellipsocephalus" is approximately oval in shape and markedly convex. It has opistoparian facial sutures that are directed slightly outward from both front and back of the eyes. The glabella has approximately parallel, slightly concave sides and is rounded frontally. Lateral furrows are indiscernible, as is the occipital ring. The palpebral lobes are not distinctly separated from the narrow occular ridges. The preglabellar field is somewhat inflated and librigenae are half as wide as the fixigenae. Some species have genal spines (as in "E. sanctacrucensis"), whereas in the most common species ("E. hoffi") the genae lack spines and are only slightly angular posterolaterally. "Ellipsocephalus" has 12 thoracic segments and the pygidium is 4× wider than long.
Behaviour.
"Ellipsocephalus" and some other primitive micropygous Cambrian genera, such as "Bailiella", enroll differently from other trilobites so that the posterior thorax segments and pygidium bend under the thorax. This is called "double enrollment".