334 | NEW YORK STATE MUSEUM 
To Sarle’s comprehensive statement: ‘ Regarding its [Hughmilleria] 
resemblance to Eurypterus, it might be said that, but for the marginal 
position of the eyes and relatively large chelae, this form would easily be 
mistaken for a species of that genus ”’ [op. cut. p. rogo], we may add from 
the results of our investigations that the facets of the eyes, the character 
of the opercular appendage and the cordate metastoma are features indica- 
tive of a closer relationship to Pterygotus and that we therefore agree with 
Sarle that it belongs in one group with the latter genus and Slimonia. 
Hughmilleria is a good genus that requires distinction as being of a 
primitive or generalized character, through which it has points of simi- 
larity with a number of other genera. It is certain that, notwithstanding 
its exterior similarity to Eurypterus, it points, by virtue of its cordate 
metastoma, the intramarginal to marginal position of the compound eyes, 
the slightly longer preoral appendages, its slender body, less developed 
swimming legs and the opercular appendage, to the path of development 
taken by Pterygotus after separation from its common ancestor with 
Eurypterus. We consequently find the critical.characters of Hughmilleria 
in the same features as did Sarle and Clarke,’ notably those evinced in 
the preoral appendages and marginal eyes, as well as in the other features 
cited, but with the difference that we take them as denoting a primi-. 
tive condition. This view is strongly supported by the ontogeny of 
H. shawangunk, for the great similarity of its nepionic and mature 
growth stages is another proof that Hughmilleria has progressed less 
beyond the common ancestor of the eurypterids than either Pterygotus 
or Eurypterus. 
contrast to their respective lengths, are proportionately more robust, and each joint, 
from the third to the sixth inclusive, carries a pair of ventrally and distally articulated 
slender, curved spines. It is doubtful if any species of Pterygotus has spines on these 
appendages; certainly, in several species in which these limbs have been found 
apparently well preserved, they are lacking. 
1 The senior author follows Sarle in the preliminary description of the Otisville fauna 
in seeing in the larger preoral appendages and the marginal eyes the critical differences 
between Hughmilleria and Eurypterus. 
