SI" PPLEM i ; . X 1 A RV. 

 Stylonurus excelsiok. 



page li)8 ) 

 PLATE XXVI. ant. PLATE XXVI I 



Through the kindness of Mr. R. D. Lacoe, of Pittston, Pennsylvania, the 

 type specimen of Dolichocephala Lacoana, Claypole (Proceedings A hut. Phil. Soc, 

 vol. 21, p. 236), lias 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 douht of then- 

 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 v, Inch 

 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, 



