340 NEW YORK STATE MUSEUM 
The telson agrees in its slender, spinelike outline with that of Euryp- 
terus. But while that of Eurypterus is flat on the dorsal side and bears 
a carina on the ventral side, that of H. socialis is flat on the 
ventral side and carinate on the dorsal. 
Horizon and locality. Pittsford shale at Pittsford, N. Y. 
Hughmilleria socialis var. robusta Sarle 
Plate 63, figure 16 
Hughmilleria socialis var. robusta Sarle. N. Y. State Palaeontologist 
Rep’t. i902. p. 1097, pl. 21, fig. 1, 2 
A tew fragments have suggested the presence of a larger variety of 
socialis in the Pittsford shale on which the following notes were made 
by Mr Sarle: 
What appears to have been a varietal form of Hughmilleria 
socialis is represented by a nearly entire abdomen, two first ring 
segments and an imperfect metastoma. 
The features which distinguish this form are: its larger size; pro- 
portionately much greater breadth; the greater convexity of the dorsal 
posterior edge of the first ring segment and, in some cases, the division 
cf this edge into two, broad smooth lobes; the more noticeable contraction 
of the abdomen at the 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 seg- 
ments 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 segment 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 
most 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 of H. socialis, but larger indi- 
viduals of that species seem to show the same relative proportions as the 
