408 NEW YORK STATE MUSEUM 
we place the Limulava with them their definition has to be completely 
changed. | 
[n the Eurypterida the cephalothorax bears six pairs of appendages, the 
first of which are chelate antennae or chelicera; these are apparently absent in 
Sidneyia inexpectans, where there are only five pairs, the 
first of which consists of simple antennae. In Slimonia the corresponding 
pair of legs is also tactile and the antennae of Sidneyia apparently bore 
coxae, so that the character of the first pair of legs would not constitute a 
difference of more than generic value. Chelicera, however, are character- 
istic of the Eurypterida, and if Sidneyia is an eurypterid, it is to be assumed 
that these, often delicate organs, will be found on further research. The 
third pair of legs is one of the remarkable features of this organism. It is 
described as “ multichelate,’’ or as possessing “‘broad, strong joints in 
small specimens, and in large specimens it is developed into peculiarly 
constructed and complex chelate terminal sections; this 1s formed of 
twelve or more joints of a forward curving appendage to which are attached 
on the anterior side long spines carrying numerous smaller spines on the 
margin opposed to the main body of the appendage.’ If indeed the leg 
consists of two jointed appendages, as reproduced in op. czt. pl. 4, figures 1 and 
4, then we have here a biramous leg such as would be characteristic of the 
Crustacea in contrast to the Merostomata, and a feature which indicates 
that the fossil 1s a crustacean rather than an arachnid. The long blade- 
like appendages resemble those of the legs of Stylonurus excel- 
sior and Echinognathus clevelandi and might, like the 
latter, have served to make a swimming organ of the third pair of legs. 
There is still a bare possibility that they are analogous to the male clasping 
organ observed by Holm on the second walking leg of Eurypterus 
fischeri and which had a sexual function. However that may be, 
these complex legs of Sidneyia are important in showing a certain advanced 
adaptation of the genus in the form of these organs. The last pair is de- 
scribed as short and bearing an outer, broad joint or palp fringed with five 
branchial setae or spines. This is another character entirely foreign to 
the arachnids and ascribable to the crustaceans. 
