| Smallest specimen observed: | millimeters | |
| Length of carapace | 5.1 | |
| Width of carapace | 5.1 | |
| Length of eyes | 1.9 | |
The largest specimen observed is but slightly larger than the type.
Horizon and locality. Shawangunk grit at Otisville, N. Y.
Observations. The carapace of this species does not bear the typical expression of any genus; its aspect is rather suggestive of several; viz, Pterygotus, Slimonia and Dolichopterus. The type specimen in which the outline is more rounded than in the rest may be well compared with Pterygotus, while the approach of the eyes to the anterior corners, the quadrangular outline of the carapace and the frontal rim are quite likely to suggest Slimonia. The lateral eyes, however, although possessing an elliptic outline as those of Pterygotus and Slimonia, are quite obviously not furnished with a visual surface extending over the whole prominence as in those genera, but with one that is crescent-shaped as in the genera more closely allied to Eurypterus. This, taken in connection with the fact that the eyes are distinctly within the margins, necessitates a reference to the latter group of genera. This granted, the identification of the species with Dolichopterus becomes imperative, for the squarish outline, the position of the eyes in the corners, their relatively large size and the broad border of the carapace are features which are combined only in the genotype of Dolichopterus. We may add that the semielliptic outline of the eyes, also a very characteristic feature in all well preserved specimens of the present species, are repeated in D. macrochirus.
The youngest specimens are of special interest in this connection; for they lack the frontal angular extension which constitutes a difference from D. macrochirus although it is only a further development of the broad frontal rim common to the young of D. otisius and to the genotype. The young [pl. 46, fig. 4] is hence still more like Dolichopterus: in fact it has the typical expression of that genus in every particular.
