Hall fully recognized that the last postoral limb differs from the corresponding organ of all other eurypterids in the development of the ninth segment into a broad expansion like an oar blade. These last limbs are not only very long, for when fully turned back they would have nearly reached the penultimate postabdominal segment, but also rather flexible and expanded in all segments, most markedly however in the last four. The coxa of this leg, which is fairly well shown in the type and still better in the specimen from Litchfield, differs in outline from those of other eurypterids being much longer in anteroposterior direction.[1]
The coxa is subrhomboidal in shape (its short posterior side only half as long as the long inner edge), with a long curved neck leading to the manducatory edge. The second and third segments are short, ringlike, especially so the third, while the fourth is distinguished from all others by its length, it being twice as long as each of the two following segments and four times as long as the preceding one. It is twice as long as wide. The fifth and sixth segments are of subequal dimensions, each nearly one fourth longer than wide. The seventh and eighth segments are broad and relatively short, their longitudinal and transverse diameters being about equal. Their outer edges are obscurely serrate. The lobe of the seventh segment which is narrowly triangular in Eurypterus, is here produced into a leaflike process, which in length equals the segment. The eighth segment, which is the palette in Eurypterus and Pterygotus, is in this genus of similar form as the preceding segment. The ninth segment, the small "claw" in other eurypterids, has here assumed the bladelike shape of the eighth segments in Eurypterus and Pterygotus. It is oval in shape, with its extremity somewhat drawn out, longer than the preceding segments, one and one half times longer than wide. Its outer margin is coarsely serrate, the serrations directed obliquely forward and convex on the outer side. The metastoma has been described by Hall as "lyrate, with the anterior margin
- ↑ This elongation is of course shared by the metastoma and obviously induced by the relatively great length of the carapace. But the mouth is further forward in this species than in other genera.
