Carapace elongate oval in outline, broadest in the posterior fourth, whence it contracts to half the width at the frontal margin. Its length and greatest width are but slightly different. The lateral margin is most convex at the broadest portion of the carapace which is frequently somewhat expanded into a kind of cheek. It becomes gently convex more anteriorly and passes rather abruptly at the antelateral angles into the more or less projecting frontal margin. The postlateral angles are well rounded and the posterior margin is deeply concave in the middle. The frontal border is furnished with a row of 8–16 acute denticulations which are longest in the middle and decrease in size toward the lateral ends. The serrae are directed obliquely upward. The lateral margins are bordered by a thickened rim.
The upper side of the carapace is highly sculptured. Its most prominent parts are the big bulging compound eyes. The portion of the carapace in front of these is flat but rises in the middle to a large subcircular mound, bearing tubercles of greater size than those forming the ornamentation of the rest of the carapace. Oval, sharply set-off cheeklike ridges extend backward from the lateral eyes to near the posterior margin, and from the intervening depression, midway between the lateral eyes, rises the very prominent small mound bearing the ocelli. The underside of the carapace bears a broad and thick doublure which is widest along the frontal margin and there exhibits a deep concentric furrow.
The lateral eyes are very large (one third the length of the carapace), forming projecting elliptical bodies that lie near the lateral margin and parallel to the latter in their major axis, thus converging strongly forward. Their posterior extremities lie approximately on the transverse bisecting line. The visual surface is crescent-shaped and narrow; its horns approach each other on the inner side. The eye mound overtops the visual surface considerably and forms apparently an overhanging ridge on the inner side of the visual surface so that the latter frequently disappears entirely in compressed specimens.
The ornamentation of the carapace consists of small tubercles which
