109S NEW YORK STATE MUSEUM 



second ring segment; and the more rotund form of the 

 metastoma. 



The abdomen found lies in the shale dorsal side up, showing 

 the anterior nine segments well preserved. The second and 

 third ring segments are partially disconnected. The breadth 

 of the preabdomen at the widest point, or between the third 

 and fourth segments, is 51 mm, its length 56 mm, the breadth of 

 the first ring segment is 42 mm, of the second 30 mm. The dorsal 

 posterior edge of the first ring segments is entire and very 

 noticeably convex. In each of the isolated ring segments a 

 broad, deep notch produces a bilobation of this edge. A line 

 of pittings close to this edge shows this feature to be natural. 

 The proportions of the more perfect of these segments are: 

 breadth 43 mm, length of the dorsal side 22 mm, length of the 

 ventral 11 mm, length of the postlateral lobes 8 mm. The 

 metastoma associated with one of these segments is apparently 

 of a smaller individual and lacks the anterior notched end. 

 At the widest part it measures 14 mm and, from there to the 

 posterior end, 14 mm. 



It was at first thought that the distinctive features of these 

 specimens might be merely old age characters ofH. socialis, 

 but larger individuals of that species seem to show the same 

 relative proportions as the smaller. However, it is considered 

 that the differences shown by the incomplete material of the 

 collection are not, of themselves, sufficient to warrant the found- 

 ing of a distinct species. 



Genus etjrypterus DeKay. 1825 

 Eurypterus pittsfordensis sp. nov. 



Plate 10, fig. 7; 15, fig. 1-3; 16-23: 24, fig. 2-5; 25, fig. 2, 5, 6 



This species is comparatively rare and is not represented in 

 the collection by any entire individuals. There is however 

 sufficient material to enable its main features to be correctly 

 determined. 



The entire animal is large and robust, and broadest at about 

 the third segment. The cephalothorax is two thirds as long 

 as broad, eyes of medium size, appendages heavy. The pre- 

 abdominal and postabdominal portions are not strongly differ- 



