Bas: 
CO. D. Walcott—New Genus of the Eurypterida. 215 
joint (1) and the anterior portions of (2) and (8) show the 
seale-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. Hach 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 back- 
ward and inward. ey 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. 
Was not less than 45 or 50 in length, and the approximate 
width 15™ 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 EKurypterida has not been repre- 
sented 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 dis- 
covery of a fragment of the test of a Pterygotus in his étage D, 5, 
Am. Jour. ae Serres, Vou. XXIII, No. 135.—Marcg, 1882. 
