154 NEW YORK STATE MUSEUM 
this Cambric progenitor; the carapace, preabdomen, postabdomen and 
telson exhibiting the same general characters and number of component 
parts. Notwithstanding this conformity in structure Strabops presents 
a number of distinctly primitive characters which indicate its closeness 
to the archetype of the eurypterids. We see the most important of these 
in the lack of differentiation 1n width and length between the preabdominal 
and postabdominal segments, the contraction of the postabdomen taking | 
place so uniformly that the conventional division between body and tail, 
so evident in all later eurypterids, is here still entirely undeveloped. The 
postabdomen, always a slender part of the body with much lengthened 
posterior segments in later forms, is here short and broad, the segments 
not at all increasing in length backward. Altogether, all abdominal seg- 
ments retain a highly primitive and simple aspect in their appearance as 
uniformly narrow straight bands that hardly bend forward at the lateral 
extremities. The first tergite, however, has progressed in development 
bevond the others, and, as in the Siluric genera, is more closely connected 
with the carapace than with the abdomen, and 1s distinctly bent forward 
at the extremities. 
The carapace is distinguished from that of the Siluric descendants 
by its remarkable shortness, or relatively very small size which may also 
constitute a primitive feature. On the other hand the doublure or rim of 
the underside is very broad, suggesting the genus Stylonurus. The eyes 
are especially notable for their small size and circular outline. 
The telson spine is short and plump, and thus in correspondence to 
the short compact body. 
Of the limbs but a single fragment is shown, and this is too small 
to indicate their character. Doubtless they correspond in lack of differ- 
entiation with the dorsal test and were probably all of simple and similar 
form, slightly increasing in length posteriorly. Strabops has served in our 
effort to reconstruct the archetype of the Eurypterida. 
‘This shortness may be partly due to a fore and aft foreshortening, as indicated 
by the pushing of the first tergite under the carapace and by the fold at the frontal 
margin. 
