sons. As no entire specimen has been obtained, we are not in position to say whether all these parts belong to but one or to several species. We have referred them provisionally to one species since the carapaces do not exhibit differences of sufficient importance to base distinctions upon, though they undoubtedly represent different growth stages. We have selected the largest and most perfect carapace [pl. 82, fig. 6] as the type and derive from this the following description:
Description. Carapace approaching a circle in outline, with a posterior segment cut off, so that the length is one fifth shorter than the width. The greatest width is in the anterior half, just behind the eyes. The frontal margin and the greater portion of the lateral margins form a continuous subcircular curve, the posterior fourth of the lateral margins slightly concave and the posterior margin nearly straight. The postlateral angles are approximately right ones. A narrow flat margin with a thickened rim surrounds the carapace except where the eyes are situated where it is presumably continuous and turned under. This margin widens near the postlateral angles. The posterior margin is also furnished with a narrow flat border. The carapace appears to have been quite convex before compression. The eyes are very large (one half the length of the carapace), of elliptic outline, hardly projecting, and situated at the well-rounded antelateral corners. Traces of the facets are noticeable. The surface is ornamented with contiguous, low broad tubercles. The first tergite is very short (11 times as wide as long), its posterior margin concave in the middle, the lateral margins rapidly diverging and curved. The surface exhibits the same ornamentation as the carapace.
Several tergites have been observed of a Pterygotus exhibiting the same typical Pterygotus-sculpturing as the carapace of this species, though more pronounced. One of these, with much extended lateral "ears" is reproduced on plate 82, figure 8. Some fragments indicate that this species attained the gigantic proportions of the Bertie waterlime species and that the smaller forms are but early growth stages. The relatively very great size of the lateral eyes points to the same conclusion.
