148 NEW YORK STATE MUSEUM 
and any of the other groups of arthropods and they would derive the 
Arachnida through the Merostomata from primitive crustaceans. Laurie 
[Recent Additions, etc. p. 117] however, has pointed out that the relation- 
ship of the eurypterids to the Crustacea is not so evident, as they 
show no special points of affinity with any one group. ‘ The absence 
of that special modification of three pairs of appendages to serve as 
mouth organs, which is characteristic of all Crustacea except the Ostra- 
coda, indicates that their point of union must have been very low down 
the crustacean stem, and the very definite number of segments and 
arrangements of appendages in the Eurypteridae indicates on the other 
hand that thev are removed a considerable distance from any such primi- 
tive type.” The fixation of the number of segments in the Cambric 
eurypterid Strabops is significant as indicating that at this early date 
they were already far removed from the common ancestor with an indefi- 
nite number of segments. 
As the most primitive and earliest crustaceans, the trilobites, are 
clearly not ancestrally or otherwise closely related to the eurypterids 
and the latter even in the Cambric are far removed from any possible 
synthetic ancestors, it is a fair question whether it is not proper to look 
for more primitive arthropods than the crustaceans as ancestors of the 
eurypterids. We have in mind now the investigations of Bernard [1896] 
who disputes the relationship of the merostomes to the crustaceans on 
one hand and to the arachnids on the other, and states that “As arthro- 
pods, no relation whatever exists between them; as segmented animals, 
however, they are both derivatives from the chaetopod annelids, but 
along different and opposite lines of specialization.’’ Bernard derives the 
Crustacea from a bent carnivorous annelid, a view which Beecher regards 
as partly verified by his discoveries concerning the ventral anatomy of the 
trilobites, and it is therefore worthy of consideration in this place. If we 
consider the absence of anything in the ontogeny of the eurypterids that 
would suggest a crustacean nauplius stage, the admitted absence of all 
crustacean features in the adult forms, and the equal absence of all crus- 
