THE EURYPTERIDA OF NEW YORK IQgQ 
of the two halves of this plate being fused. It is slender, being about one 
fourth as wide as long and does not quite reach the posterior edge of the 
sternite. The anterior end is slightly constricted where it fuses with the 
sternite, and the distal is tapering. The male appendage is confined to the 
operculum. In the material of the collection is a single specimen showing 
the exterior, the others showing the internal form only. It was evidently 
small, about one fifth the length of the operculum by which it is surrounded. 
The body is covered with comparatively coarse, imbricating crescentic 
scales, most distinct on the sternites and swimming arms. When the 
integument of the metastoma and paired appendages are scaled away, 
there remains a punctate surface. The specimens found show that the 
size of these animals averages from 20 centimeters to 30 centimeters. A 
fragment of the third joint of a swimming arm was found, however, which 
appears to have been part of an individual over 60 centimeters in length. 
In the outline, size and proportions of carapace (length : width as 2:3) 
this species resembles E. lacustris more than any other form. More- 
over, the abdomen and the legs appear not to have been very different, but 
the telson is notably longer and more slender than in E. lacustrisor 
in any other of our species of Eurypterus. 
Before us are carapaces showing that this species grew still larger 
than the type specimens indicate. One of these measures 54 x 89g mm, 
another is 58 mm x circa 98 mm. | 
One of the original figures [op. cat. pl. 10, fig. 7] shows three ends of 
appendages with thick, clawlike terminal segments. On the left side, how- 
ever, two endognathites are shown with thin spinelike terminal segments. 
As other specimens show that the endognathites did not possess such 
clawlike segments at their extremities, it is probable that Sarle’s inter- 
pretation of the specimen is not correct. An inspection of the original 
shows that the supposed terminal segment on the middle line of the figure 
is one of the chelicerae, but the two others on the right hand side are oval 
prominences with a median sulcus but without separation of the test. 
We surmise, therefore, that they are the upper views of the first seg- 
ments of endognathites which are displaced. A corrected figure is here 
given on plate 13, figure 6. | 
Horizon and locality. Pittsford shale, Pittsford, Monroe co., N. Y. 
