THE EURYPTERIDA OF NEW YORK 409 
The carapace is stated to possess a large epistoma and to lack a metas- 
toma. In eurypterids the epistoma is only known in the Pterygotus- 
Slimonia group. It is there a separated part of the marginal shield and 
originated from a part of the carapace being bent over, as shown by the 
direction of the sculpture. The organ figured as epistoma of Sidneyia 
(op. cit. pl. 5, fig. 3) is hardly comparable to the epistoma of Pterygotus, as 
it is not separated by sutures from the marginal shield. The view referred 
to is obviously a dorsal one and there seems to us much probability that 
‘ 
the large “‘ epistoma ”’ may prove to be the anterior part of the carapace 
pushed out of position. 
_ There is nothing visible in the figures of these finely preserved remains 
to suggest the presence of a metastoma. The latter is distinctly a char- 
acteristic and important organ of the order Eurypterida. If it is actually | 
absent in the Limulava this fact would militate against the inclusion of 
the latter in the eurypterids. 
The most important differences between the Eurypterida and Limulava 
appear, however, in the constitution of the abdomen. The abdomen of 
the Eurypterida consists invariably of six tergites on the dorsal side, to 
which correspond five sternites on the ventral side, and six ringlike post- 
abdominal segments. Sidneyia, however, appears to possess as many 
segments on the dorsal as on the ventral side. The operculum or first 
ventral plate which covers both the first and second segment and which 
bears the genital appendage, was hence not yet developed. This would be 
a most primitive condition, as compared with the eurypterids, and constitutes 
a difference of ordinalrank. Sidneyia is further described as bearing branchiae 
on nine segments. The Limulava have accordingly nine abdominal segments 
and but three postabdominal segments, for the gill-bearing ventral segments 
must be movable plates.of the character of sternites’ This is also a differ- 
ence of ordinal rank, for the number and division of segments in the Euryp- 
terida is absolutely fixed, but if Sidneyia is in any way related to the ances- 
tral stock of the Eurypterida it is bound to throw most interesting light 
on the morphogeny of the abdomen. The gills themselves must also have 
