Page:The Eurypterida of New York Volume 1.pdf/347

 smaller. However, it is considered that the differences shown by the incomplete material of the collection are not, of themselves, sufficient to warrant the founding of a distinct species.

We have not obtained any further material that would qualify the inferences here set forth.

Horizon and locality. Pittsford shale at Pittsford, N. Y.

Description. Carapace semielliptic, length and basal width subequal, lateral margins gently curved, subparallel, frontal margin bluntly angular so as to form a triangular front to the carapace. Posterior margin straight transverse or very slightly concave; genal angles roundish rectangular.

Lateral eyes large (a little more than one third the length of the carapace), submarginal, oval in outline. Ocelli subcentral, their tumescence between the posterior ends of the lateral eyes.

No ornamentation has been observed on the carapace.

Horizon and localities. Frankfort shales. The great majority of the specimens are from the Dettbarn quarry at Schenectady, where in one layer the species is quite common. A few carapaces have also been found at Duanesburg and Rotterdam Junction, Schoharie county.

Remarks. The form of the carapace is subject to much variation in outline, obviously through the stretching and wrinkling of the thin, drifted integuments in various directions. The carapace selected as the type [pl. 85, fig. 11] is smooth and but little distorted. When the test is completely flattened out, the lateral eyes are seen to be separated from the margin of the carapace by a narrow strip, half as wide as the eye, contracted forward and broadening backward as in the genotype.

The type measures 17.5 mm in length and 20 mm in width. The eyes are 7 mm long. Several carapaces indicate that this species reached much larger dimensions than its supposed later allies. The original of plate 85, figure 16 is 58 mm wide and 42 mm long. Its lateral margins are completely flattened out and the specimen somewhat compressed in the axial direction.