272 NEW YORK STATE MUSEUM 
Smallest specimen observed: millimeters 
Length of carapace... ... ee cece cee cece eee nt eneees 5.1 
Width of carapace... kee eee cece te eee tenn eees 5.1 
Length of €yeS.. eee ce ee eee eee teens 1.9 
The largest specimen observed is but slightly larger than the type. 
Horizon and locality. Shawangunk grit at Otisville, N. Y. | 
Observations. The carapace of this species does not bear the typical 
expression of any genus; its aspect is rather suggestive of several; viz, 
Pterygotus, Slimonia and Dolichopterus. The type specimen in which 
the outline is more rounded than in the rest may be well compared with 
Pterygotus, while the approach of the eyes to the anterior corners, the 
quadrangular outline of the carapace and the frontal rim are quite likely 
to suggest Slimonia. The lateral eyes, however, although possessing an 
elliptic outline as those of Pterygotus and Slimonia, are quite obviously 
not furnished with a visual surface extending over the whole prominence 
as in those genera, but with one that is crescent-shaped as in the genera 
more closely allied to Eurypterus. This, taken in connection with the 
fact that the eyes are distinctly within the margins, necessitates a reference 
to the latter group of genera. This granted, the identification of the spe- 
cies with Dolichopterus becomes imperative, for the squarish outline, the 
position of the eyes in the corners, their relatively large size and the broad 
border of the carapace are features which are combined only in the geno- 
type of Dolichopterus. We may add that the semielliptic outline of the 
eyes, also a very characteristic feature in all well preserved specimens of 
the present species, are repeated in D. macrochirus. 
The youngest specimens are of special interest in this connection; 
for they lack the frontal angular extension which constitutes a difference 
from D. macrochirus although it is only a further development 
of the broad frontal rim common to the young of D. otisius and 
to the genotype. The young [pl. 46, fig. 4] 1s hence still more like 
Dolichopterus: in fact it has the typical expression of that genus in every 
particular. 
