SUPPLEMENTARY. 
Sttlonurds excelsior. 
(See page 158 ) 
PLATE XXVI, AND PLATE XXVI A. 
Through the kindness of Mr. R. D. Lacoe, of Pittston, Pennsylvania, the 
type specimen of Dolichocephala Lacoana, Claypole (Proceedings Amer. Phil. Soc., 
vol. 21, p. 236), has been communicated for comparison with S. excelsior. This 
specimen is from the Catskill group, of Meshoppen, Wyoming county, Pennsyl¬ 
vania, and consists of the greater portion of a cephalon of slightly larger 
dimensions than the original of S. excelsior, and shows so close a similarity to 
the latter in outline and surface features that there can be no doubt of their 
specific identity. 
The surface of Mr. Lacoe’s specimen has been somewhat distorted by the 
compression of the carapace upon the underlying parts, and although this 
portion is not as well preserved as in the type specimen, it shows a single 
feature of great importance, not seen in the latter. The conspicuous and 
comparatively smooth ridge passing between the eyes, is divided at its rounded 
posterior extremity by a sharply incised longitudinal line, on each side of which 
lies a distinct ocellus. This feature has not before been noticed in specimens of 
Stylonurus, and it affords an additional point of alliance between this genus and 
the genera Eurypterus and Pterygotus. 
The lower surface of the specimen as it came into our hands showed a few 
indications of the cephalic appendages; these traces have been followed up 
and the organs carefully worked out. These, as far as they remain, are 
quite perfectly preserved, and appear to lie in their normal position beneath 
the carapace. 
The first or anterior pair of gnathopods is represented by the impression 
upon the upper left edge of the specimen, of two short joints, followed by a 
longer joint, which may have been chelate. This part is represented in the 
figure having been drawn from a cast in gutta-percha. Unless this appendage 
has been detached from its proper position it must have been somewhat longer 
than the members of the second pair. The right leg of the second pair is 
preserved nearly entire, a portion of its basal joint being deeply buried in the 
matrix beneath the next succeeding appendage. The portion exposed measures 
40 mm. in length to the distal articular surface, and about 20 mm. in greatest 
width. The inner margin bears a broad mandibular flange, which is serrate 
upon the edge, and there is evidence of another such process partially concealed 
in the matrix. The remaining portion of this appendage is 90 mm. in length. 
