I52 . NEW YORK STATE MUSEUM 
*P. macrophthalmus Hall 
*P. monroensis Sarle 
*P. nasutus nov. 
*P. prolificus nov. 
VIII 
SYSTEMATIC ACCOUNT OF THE EURYPTERIDA 
Class ARACHNIDA 
Subclass MEROSTOMATA (Dana) Woodward 
Order HURRY PTERIDA Burmeister 
Family EURYPTERIDAE Burmeister 
Genus STRABOPS Beecher rgo1 
Strabops thacheri Beecher 
Plate 1; plate 4, figure 5; plate 13, figure 2 
Strabops thacheri Beecher. American Journal of Science, n. s. 12:365, 1901 
-An euryptefid of extraordinary interest because of its age and com- 
pleteness is a specimen obtained in the Cambric Potosi limestone of St 
Francois county, Missouri, which was studied by Prof. C. E. Beecher, 
and made by him the type of the genus and species: Strab ops 
thacheri. Professor Beecher, evidently without his own knowledge 
had the use only of the relievo of this specimen and the counterpart has 
been found by the authors in the collections of Columbia University. The 
specimen 1s so preserved that the interior view of the dorsal side is shown 
in both cast and mold, and the latter is obviously the more distinct. Had 
it been at the disposal of the describer it would probably have prevented 
some evident misconceptions of structural details. The intaglio, cleaned 
with potash [pl. 4, fig. 5] and sharply cast [pl. 13, fig. 2], exhibits quite 
distinctly all true structure lines. 
The specimen was correctly recognized by Dr Beecher as suggesting 
the genus Eurypterus. Its differences from the latter genus which, as 
such, constitute the generic characters were set forth by him as follows: 
The cephalothorax is comparatively shorter and wider than in Euryp- 
terus, the eyes are further forward, nearer together, and more oblique, 
and besides the telson but 11 abdominal somites can be determined on the 
dorsal side, instead of 12, as in Eurypterus. These differences are con- 
