90 NEW YORK STATE MUSEUM 



Pterygotus inexpectans nov. 



Description. Cephalothorax trapezoidal in general outline, about 

 one-ninth wider than long; the lateral margins slightly signioidal, 

 being concave in the posterior, and convex in the anterior half, pro- 

 ducing a slightly forwardly expanding shape of the carapace. 

 Anterior margin well rounded, and posterior margin nearly trans- 

 verse, slightly bent forward at the subrectangular postero-lateral 

 angles. The surface seems to have been flat in the posterior half 

 and gently convex in the anterior, with a fairly abrupt decline at 

 the frontal margin. The lateral eyes are very prominent, but rela- 

 tively small (a little more than one-fifth the length of the carapace), 

 subelliptic in outline and situated in the antero-lateral corner of the 

 carapace. The ocelli are large and distinct, and situated on a line 

 connecting the posterior extremities of the compound or lateral eyes ; 

 or about two-fifths of the length of the carapace from the anterior 

 margin. The marginal thickening is well developed, about i mm 

 wide. The surface shows traces of low tuberculation. 



Measurements. Greatest width (behind compound eyes) 66 mm; 

 basal width 62 mm ; length 53 mm ; greatest height 8 mm. Length 

 of compound eyes 10.5 mm ; width of same 6 mm. 



Horizon and locality. . Upper tree-fern beds in Oneonta sand- 

 stone at Gilboa, Schoharie county, N. Y. 



Remarks. This is the first Pterygotus found in the Devonian of 

 New York. Compared with its American Silurian congeners, 

 especially P. buffaloensis and m a c r o p h t h a 1 m u s , 'it is 

 distinguished by the relatively small size of the compound eyes and 

 the sigmoidal curve of the lateral margins, or the forward expansion 

 of the carapace; features in which it shows a certain approach to 

 the Old Red sandstone forms of Scotland, and particularly to the 

 remarkable S 1 i m o n i a a c u m i na t a , which not only possesses 

 like small, but prominent lateral eyes, but also a slight lateral expan- 

 sion of the carapace in the anterior portion and a like strongly 

 developed thickening of the margin. 



Both the discovery of the carapace and leg parts of the gigantic 

 S t y 1 o n u r u s excelsior near Andes in the Catskill beds, and 

 the finding of this Pterygotus which, judging from the carapace in 

 hand, also reached a size of a foot and a half, in the underlying 

 Oneonta beds, suggest that some day there may be obtained in the 

 American equivalent of the British Old Red sandstone, in the Cats- 

 kills of New York, an eurypterid fauna as striking and important as 

 that made known by Salter and Woodward from Great Britain. 



