THE EURYPTERIDA OF NEW YORK 139 
malpighian vessels, whereas the merostomes (Limulus) and all unques- 
tionable Crustacea are devoid of these vessels.’”” He suggests that the 
arachnids also form an ancient type, and that the common origin of the 
merostomes and the arachnids must be sought for. far down in the pedigree 
of the arthropods. ‘“‘ The agreement between scorpions and eurypterids 
would then be derived from causes quite independent of close relationship, 
and perhaps from a convergence in some branches of the two stems which 
are formed by the merostomes and the arachnids.”’ 
Opposed to this, Lankester and his followers hold that the presence 
of gills and the absence of malpighian tubules are features associated 
with aquatic life, and hence of no critical classificatory value, and Laurie 
and Claus assert that the morphological value of the gills has been 
greatly overestimated. Laurie notes that the branchiae of eurypterids, 
like those of Limulus, are constructed on a type unknown amongst 
the Crustacea, and further, that structures such as these, which are the 
product of a physiological necessity, are not of much value in indicating 
close relationship. He cites as arguments against the crustacean relation- 
ship ‘“‘ the segmentation of the body and position of the genital aperture— 
which does not agree with that of any known crustacean, the absence 
of anything representing the first antennae, the chelate structure of the 
one pair of preoral appendages and the fact that there is no trace of the 
typical crustacean biramous structure of the appendages.’’ Admitting the 
relationship of the eurypterids to the arachnids, Laurie thinks that “ the 
eurypterids must be considered as intermediate between Crustacea and 
Arachnida, in the sense that they are among the most primitive arachnids, 
and therefore nearer the junction point of the two terms.’”’ Agreeing with 
the other authors as to the close relationship of the eurypterids with Limulus, 
Laurie sees a point of great morphological importance “in the fact that 
Limulus has a pair of platelike appendages on the second abdominal seg- 
ment,’’ and takes this to indicate that ‘‘ Limulus branched off from the 
eurypterid stem before the genital operculum was so highly specialized as it 
isin the eurypterids, and, consequently, before the appendage of the second 
