Page:AmJourSci 3 23 135 213-216.djvu/3
C. D. Walcott—New Genus of the Eurypterida.
joint (1) and the anterior portions of (2) and (3) show the scale-like markings observed on the fragment of the thoracic segment. If there were but one joint beyond the transverse joint (1), i. e. the basal, the entire appendage would have had nine joints, if our interpretation of the crushed joints is correct.
The long curved spines (s, s, s), are a very curious feature of the appendage and the most marked character of the genus and species. They are articulated to the posterior margin of the joints, as the latter rest flattened out in the slate or shale, and there is no evidence but that they formed a single series, as shown in the specimen and in the drawing, fig. 2. Each spine is constricted a little near its base, forming a rounded end or point of articulation; from this well out toward their pointed termination they retain an average width curving gently backward and inward. They appear to have been flattened when in a natural condition, and formed of a thin test which is rather strongly striated.
It is difficult to understand the purpose these spines served unless they are considered as having some relation to the branchial system of the animal. That they were used in securing food or carrying it to the mouth is not apparent, and no other use than the above is suggested from a study of the specimens we now have.
In the specimen of Dolichopterus macrocheirus, previously referred to, a few short, small spines are seen projecting from the posterior margins of the third, fourth and fifth joints of the third endognath. That they may represent in a greatly modified degree the spines shown in fig. 2 is not improbable. Eurypterus punctatus (Salter) Woodward, as restored in Woodward's Monograph of the Fossil Merostomata, p. 157, has a pair of long curved spines on four of the joints of the endognathary palpus, but they are represented as projecting forward, which does not appear to have been the case in the Utica slate species.
The character of the endognathary palpus of E. Clevelandi may indicate the approach to an earlier type of the Eurypterida, but from the characters shown by these remains and the fact that its size, estimating from the fragment of the thorax, was not less than 45 or 50cm in length, and the approximate width 15cm or more, it is evident that we must search deep in the strata of the Trenton group, or even lower, for the first members of the order.
As far as known to us the Eurypterida has not been represented hitherto on the American continent below the Medina sandstone of New York, and no described species is known below this horizon elsewhere. M. Barrande mentions the discovery of a fragment of the test of a Pterygotus in his étage D, 5,Am. Jour. Sci.—Third Series, Vol. XXIII, No. 135.—March, 1882.