214 NEW YORK STATE MUSEUM 



H. shawangunk Clarke, which not only possesses a like relatively- 

 broad carapace and equally inwardly placed compound eyes, but also 

 the same linear sculpture on the front of the carapace and of the 

 tergites. While, however, in H. shawangunk this linear 

 sculpture is also carried to the ventral side (see Clarke and Ruede- 

 mann, pi. 66, fig. 7), in H. phelpsae the ventral side pos- 

 sesses the angular imbricating scales ofH. socialis. 



While thus H. phelpsae and H. shawangunk are not 

 identical species as one might surmise at first glance, they are never- 

 theless much more closely related to each other than are H. phelp- 

 sae and H. socialis. This is the more remarkable in view of 

 the fact that H. phelpsae is younger than H. socialis and the 

 related H. shawangunk is, according to some authors (Van 

 Ingen, Schuchert) who would place the Shawangunk grit in the 

 Clinton or upper Medina, still much older than H. socialis. 

 The Vernon species would then appear as a probable late descendant 

 of the earlier Shawangunk form rather than of the closely preceding 

 Pittsford species. 



Pterygotus ? vernonensis nov. 



Plate I, figures i and 2 



The writer has collected two small carapaces in the Vernon shale 

 that are representative, in outline and position of compound eyes, 

 of the Pterygotus group of the eurypterids, but not identical with 

 the Pterygotus monroensis of the Pittsford shale fauna; differing 

 from the latter in being rectangular in shape with a straight transverse 

 frontal margin, while in P. m o n r o e n s i.s , judging from the 

 single specimen known, the carapace is semi-elliptic and well rounded 

 in front. 



The larger carapace is 10.5 mm wide and 7.5+ mm long, the 

 smaller one (type) is 4.5 mm wide and 4 mm long. The carapace 

 of this form is hence relatively short when compared with that of 

 other congeners. The lateral margins are nearly straight or but 

 slightly sinuous, the frontal margin gently convex and the antero- 

 lateral corners abruptly rounded. The compound eyes are placed 

 in these corners, occupying the projecting points of the latter, and 

 hence, in the larger specimen at least, appearing as narrow trunca- 

 tions of the angle. Median eyes subcentral. Surface in the smaller 

 specimen furnished with fine, closely arranged tubercles on the 

 posterior portion of the carapace; in the larger, with short, oblique, 

 parallel lines along the lateral margin. 



